We investigated effects of starvation on acid tolerance of young-of-year smallmouth bassMicropterus dolomieuiin the laboratory. Juvenile smallmouth bass, held under simulated winter conditions for up to 5 months, experienced losses in ash-free dry weight of up to 30%. However, consecutive tests failed to demonstrate any decline in the short-term (≤7 d) tolerance of these fish for pH levels in the range from 3.0 to 4.5. We discuss the implications of these findings for northern populations where young-of-year fish experience significant winter starvation, followed by short-term exposure to low pH in spring. Calcium and sodium concentration of the water and fish body size (fork length) were all positively related to acid tolerance. A doubling of fork length increased survival time at any pH by 100%. At pH 3.0, a doubling of calcium concentration increased survival time by 13% and at pH 4.0 it increased survival time by 50%. Over the pH range 3.75 to 4.0, a doubling of sodium concentration increased survival time by 8%. The strong effect offish body size on acid tolerance should be recognized and controlled in future acid tolerance experiments. It should be taken into account when laboratory tolerance estimates are used to assess the susceptibility of wild populations to acid stress.