Butyl tin compound concentrations were determined by the hydride reduction-atomic absorption technique for sixteen sediment cores from San Diego Bay, California. The results indicate that tri-, di-, and monobutyl tin are present in significant concentrations (up to 551 ug/kg dry-weight total butyl tin) in the sediment. Total butyl tin concentrations decrease with depth in the cores, and tributyl tin de-butylates directly into monobutyl tin in the sediment, with a half-life of approximately 162 days. Cores recovered from the channel entrance, where tidal flushing is good, and a recently dredged marina showed low to non-detectable (≤2 ug/kg) butyl tin concentrations. Commercial Basin, a tidally-restricted basin with dry docks currently removing butyl tin-containing hull paints, has a high butyl tin load throughout the cores, indicating bioturbation is currently occurring. Shelter Island Yacht Basin, also a restricted basin, contains butyl tin-impacted sediment, primarily due to seawater leaching of butyl tin-containing marine paints. Concentrations are significantly higher by a factor of five or greater in the top 2 cm. of sediment than in the remainder of the cores. This indicates that while bioturbation has occurred after 1975 (initial significant butyl tin-containing marine paint use), as evidenced by butyl tin compounds at depth 1 bioturbation is no longer occurring, as indicated by the significant difference in vertical distribution of the butyl tin compounds.