The bioavailability of organic contaminants in the environment has been of growing interest in recent years.  This presentation specifically addresses the bioavailability of soil- or sediment-sorbed organic contaminants to contaminant-degrading bacteria.  Sorption often reduces the rate and extent of biodegradation and many sorbed substrates are not readily available. However, sorption does not necessarily prevent biodegradation from occurring.  Studies suggest that sorbed contaminants can be degraded by microorganisms or, at least, that desorption into bulk solution is not a prerequisite for biodegradation.  The experimental evidence and proposed mechanisms of biodegradation of sorbed organic chemicals, as well as physiochemical and microbiological factors affecting bioavailability, will be critically examined.  Improved understanding of bioavailability processes will guide assessment of human health and ecological risks associated with sorbed pollutants, selection of appropriate remediation technologies, and determination of cleanup goals.