Rodemann et al. [Rodemann et al. (1987): Biochem Biophys Res Commun 145:1-9] reported that human skin fibroblasts increase their rate of protein synthesis by as much as over ninefold in response to long term exposure to 20 Hz, 8.4 mT (84 G) magnetic fields. Here we report studies of protein synthesis using an identical cell type, exposure conditions, and the same means of measuring protein synthetic rates. Our initial goal was to determine if the earlier results could be replicated, but we found an inconsistency in the earlier protocol. It exposed cells to [(3)H]leucine for 6 h prior to measuring incorporation into protein. We found, however, that 24 h is required for [(3)H]leucine to reach a steady state distribution across the cells' plasma membranes. In addition, we typically measured 100-200 cpm/thousand cells. This is four- to eightfold higher than the 19-28 cpm/1000 cells previously reported. Using these conditions, we could find no significant difference in protein synthesis rates between control cells and cells exposed for up to three weeks in an identical electromagnetic field. In addition, we investigated the effects of a 60 Hz field since that is the frequency used for electric power distribution in the United States. Again, we could find no significant effect of this field on rates of protein synthesis, even after 21 days of exposure.