Rising ultraviolet-B (UVB, 280–320 nm) radiation has been proposed as a factor which may explain nonnormal amphibian population declines. Accordingly research has been directed toward estimating the photolyase activity of several amphibian species in order to predict a species' resilience to UV damage. Unfortunately, in spite of published research which demonstrated that the activity of one of the principal photorepair enzymes, photolyase, can be induced, these estimates did not address the potential for in vivo induction by environmental factors present in situ. We show here that wood frog (Rana sylvatica) embryos exposed to periods of ambient solar radiation (1) displayed significantly different photolyase activities from embryos exposed to equivalent periods of dark; and (2) were positively correlated with the UVB fluence received in vivo. Such results suggest that previous conclusions regarding the relationship between photorepair and population decline must be reevaluated. Estimating amphibian photorepair is a complicated process, and caution must be exercised when interpreting such data.