A survey of electrophoretic variation was conducted using 74 sea otters from California and nine from Alaska. Thirty-one presumptive loci were successfully scored. Because of the severe bottleneck suffered by the population in California, we compared the level of genetic variation in this population with otters from Alaska. For both samples, 19.4% of loci studied were polymorphic with two alleles each, and heterozygosity was 4.9% (7.4% based on Hardy-Weinberg expectations). Sea otters show genetic variability levels more typical of terrestrial mammals than marine species. Comparing samples from California and Alaska, allelic and genotypic frequencies differed at one locus and heterozygosity levels were 2.2% greater in the sample from Alaska. At three loci, sea otters from California had a deficiency of heterozygotes. Local inbreeding seems to be the most likely explanation for this deficiency. Our results support the predictions of earlier models that otters from California suffered only a small loss in genetic variability.