Largemouth bass Micropterus salmoides were collected from Lake Lillinonah and Pickerel Lake, Connecticut, during three sampling periods in 1996: spring (May 14–15); summer (Jul 22–30); and fall (Oct 10–17). Total mercury concentrations ranged from 0.106 to 2.293 μg/g in Lake Lillinonah and from 0.456 to 1.762 μg/g in Pickerel Lake. In both lakes, there was a significant positive relationship between total mercury concentration and length and age during each season. Mean mercury concentrations adjusted for length were significantly different among seasons in Pickerel Lake (P = 0.0002) and Lake Lillinonah (P = 0.0006) and were 26–43% higher during spring than summer and fall in both lakes. Mean mercury concentrations adjusted for age were significantly different among seasons in Lake Lillinonah (P = 0.02) but not in Pickerel Lake (P = 0.06). In Lake Lillinonah, mean mercury concentrations adjusted for age were significantly higher during spring than during fall (P < 0.017). These results suggest that researchers may want to assess mercury concentrations in largemouth bass during standardized sampling periods so that data can be more accurately compared among water bodies and tracked over time.