This study documents changes in contamination over time at seasonal, interannual, and decadal time scales for sport fish collected in San Francisco Bay. Samples from seven fish species were prepared according to common consumption practices (muscle fillets either with or without skin) and analyzed for trace metals (mercury and selenium) and trace organochlorine contaminants (PCBs, DDTs, chlordanes, and dieldrin). In 2000, sport fish samples exceeded human health screening values for mercury, PCBs, DDTs, selenium, and dieldrin but did not exceed screening values for chlordanes. On a seasonal time scale, white croaker (Genyonemus lineatus) exhibited significantly lower PCB and lipid concentrations in spring, and a general increase in concentrations in other seasons. When monitoring data were compared among 1994, 1997, and 2000, analysis of variance indicated that concentrations of mercury, PCBs, DDTs, and chlordanes varied significantly among years for several fish species. Interannual variation in DDTs often correlated to changes in sampled fish size or lipid content among years. Interannual variation in mercury and PCBs was evident in striped bass (Morone saxatilis) but absent in shiner surfperch (Cymatogaster aggregata), leopard shark (Triakis semifasciata), and white croaker. The higher interannual variability of striped bass contaminant concentrations may result from migratory behavior and wide home ranges. Chlordanes significantly declined between 1994 and 2000 in white croaker and striped bass. Of the historical data analyzed (1986-2000), only DDT concentrations in white sturgeon (Acipenser transmontanus) showed evidence of a significant decline. Neither PCBs nor selenium showed evidence of a trend in white sturgeon. Between 1970 and 2000, mercury concentrations in striped bass showed no evidence of a trend. The absence of recent trends in mercury may result from the presence of widespread and historic sources, with use reductions occurring in the early 20th century. In contrast to mercury, apparent recent declines in fish tissue DDT and chlordane concentrations may result from use curtailment in the 1970s and 1980s.