In spite of decades of research on the effect of lime on N mineralization, there is no general agreement on whether liming stimulates or has no appreciable effect on N mineralization. A 56 day laboratory study was conducted to determine N and C mineralization in two South African acid humic soils. The two surface soils used in this experiment were collected from Eastern Cape, South Africa. The soil from Magusheni demonstration site is classified as Magwa connemara series (Humic Hapludult), and contains 270 g sand kg-1, 280 g silt kg-1, 450 g clay kg-1, 45.7 g kg-1 total C, 3.1 g kg-1 total N, 75% base saturation, 25% acid saturation, and a soil pH (saturated paste) of 4.78. The soil from Nikwe demonstration site is classified as Sweetwater newton series (Humic Hapludult), and contains 300 g sand kg-1, 260 g silt kg-1, 440 g clay kg-1, 33.6 g kg-1 total C, 2.0 g kg-1 total N, 96% base saturation, 4.0% acid saturation, and a soil pH (saturated paste) of 5.0. The soils were amended with a factorial combination of 4 rates of lime and 3 rates of manure. The lime rates were (1) a full-lime rate to raise soil pH to 6.0, (2) 66% of the full-lime rate, (3) 33% of the full-lime rate; (4) a control without lime. The broiler chicken manure rates were (1) 10 Mg ha-1, (2) 5 Mg ha-1 and (3) a control without manure. The addition of lime (lime and lime + manure treatments) to the Magusheni soil resulted in substantial N immobilization. The net in N mineralization ranged from 29 mg kg-1 in the 10 Mg ha-1 manure only treatment to 13 mg kg-1 in the full-lime rate + 10 Mg ha-1 manure treatment. Likewise, net N mineralization ranged from 12 mg kg-1 in the 5 Mg ha-1 manure only treatment to 6 mg kg-1 in the full-lime rate + 5 Mg ha-1 manure treatment. The net N mineralization following lime addition were inversely related to the amounts of evolved CO2. The CO2 evolution rates ranged from 12 mg C g-1 in the 5 Mg ha-1 manure only treatment to 19 mg C g-1 in the full-lime rate + 5 Mg ha-1 manure treatment. Similarly, CO2 evolution rates ranged from 18 mg C g-1 in the 10 Mg ha-1 manure only treatment to 26 mg C g-1 in the full-lime rate + 10 Mg ha-1 manure treatment. Correlation was used to compare relationships between mineralized C, N and other soil properties. Net N mineralized was correlated positively to amount of CO2 evolved (r = 0.63; P < 0.05) and NH4-N (r = 0.75; P < 0.001). Mineralized N was not correlated to soil pH, NO3-N, soil total C, soil total N, and C:N ratio. The amount of CO2 evolved was also significantly correlated to NO3-N (r = 0.65; P < 0.05), total C (r = 0.63; P < 0.001), C:N ratio (r = 0.45; P < 0.01), and soil pH (r = 0.43; P < 0.05). In contrast, liming had no appreciable effect on N mineralization in the Nikwe soil. Nitrogen mineralization rates ranged from 30 mg kg-1 in the 10 Mg ha-1 manure only treatment to 32 mg kg-1 in the full-lime rate + 10 Mg ha-1 manure treatment. Likewise net N mineralization ranged from 15 mg kg-1 in the 5 Mg ha-1 manure only treatment to 16 mg kg-1 in the full-lime rate + 5 Mg ha-1 manure treatment. There was some evidence that the microbial respiration rates were lower in the Nikwe soil as compared to Magusheni soil. The CO2 evolution rates ranged from 9 mg C g-1 in the 5 Mg ha-1 manure only treatment to 13 mg C g-1 in the full-lime rate + 5 Mg ha-1 manure treatment. Likewise, CO2 evolution rates ranged from 16 mg C g-1 in the 10 Mg ha-1 manure only treatment to 20 mg C g-1 in the full-lime rate + 10 Mg ha-1 manure treatment. The amount of CO2 evolved (r = 0.95; P < 0.001), NO3-N (r = 0.99; P < 0.001) and NH4-N concentrations (r = 0.49; P < 0.05) were significantly correlated to net N mineralization. Other soil characteristics, such as pH, soil total C, soil total N, and C:N ratio were not significantly correlated to mineralized N. Furthermore, the amount of CO2 evolved was significantly correlated to NO3-N (r = 0.95; P < 0.001), NH4-N (r = 0.44; P < 0.05), total C (r = 0.42; P < 0.05), C:N ratio (r = 0.41; P < 0.05). The soil pH increased with lime application. However, manure application caused the soil pH to increase in the Magusheni soil or decrease in the Nikwe soil. The main factor affecting pH changes in the manured soils seems to be nitrification. The percent inorganic N that was in the nitrate-N form for the 5 Mg ha-1 and 10 Mg ha-1 manure only treatments was between 60 to 72 % in the Magusheni soil compared to 97% in the Nikwe soil. This suggests that N transformations following chicken manure additions are potentially acidifying in nature, provided that all of the NH4+ produced is nitrified. Liming increased C mineralization in both soils, but the relative increases were higher in the Magusheni soil (13 to 57%). Liming enhanced N immobilization in the Magusheni soil, but showed not detectable effects on N mineralization/immobilization processes in the Nikwe soil. These results suggest that liming caused a considerable increase in the microbial population in the Magusheni soil, which in turn increased the demand for N by this rapidly growing population. In the Nikwe soil, N immobilization did not occur because there was sufficient N to meet the microbial N demand during decomposition. Soil acidity by itself did not limit N mineralization.