Although the potential negative effects of increased ultraviolet-B (UV-B) radiation on early life stages of aquatic organisms are widely recognized, possible synergistic effects with other stressors have seldom been studied outside the laboratory. We investigated the effects of UV-B radiation and pH on hatchability and early development of moor frog Rana arvalis eggs in the field and in laboratory experiments conducted during April 1998 and April 2000 in central Sweden. 2. In the field experiments, no evidence was found for reduced hatchability or increased frequency of developmental anomalies of embryos exposed to ambient levels of UV-B compared with embryos shielded from UV-B radiation. 3. Hatchlings shielded from ambient UV-B radiation did not grow larger than their exposed full-sibs, giving no support to the hypotheses that (i) the repair of cellular UV-B damage might be energetically costly nor (ii) that UV-B-induced photoproducts directly reduce growth. 4. Although low pH (50) reduced hatchability, increased frequency of developmental anomalies and reduced early embryonic growth in R. arvalis, there was no evidence for synergistic effects of pH and UV-B on any of these traits. 5. The lack of UV-B radiation effects on the development of R. arvalis embryos cannot be ascribed to relatively low effective daily doses of radiation (c. 043 kJ m2) during the field experiments, as in the laboratory even higher doses at UV-B 125 kJ m2 and 158 kJ m2 (all DNA weighed) had no negative effects. 6. These results suggest that current levels of UV-B radiation in northern Europe are not likely to reduce fitness in natural populations of the moor frog, even in areas already stressed by acidity.