A study of allozymes in 30 species from the three genera of snails in the family Partulidae was undertaken to examine the phylogeny of, and evolutionary rates in, the genus Partula from the Society Islands, French Polynesia. Genetic identities (I) between congeneric species are generally high, with 42% of the I values being greater than 0.85, and 24% above 0.90. Levels of allozymic similarity are therefore of little use for inferences about reproductive relationships. Identities between species from the same island are particularly high, and phylogenetic analysis suggests that the radiation of Partula in the Society Islands can be accounted for by a single colonization of each island. In general, the inferred sequence of colonization is consistent with geological information about the origins of these volcanic islands. The phylogeny, and the ages of the islands, suggest an average rate of allozymic divergence (change in Nei's D) of 0.126 per million years. The threefold variation in estimated rates of change within Partula, and the comparison of our results with estimates from other taxa, suggest that the `molecular clock' in Partula is erratic.