Immunological comparisons of a larval hemolymph protein enabled us to build a tree relating major groups of drosophiline flies in Hawaii to one another and to continental flies. The tree agrees in topology with that based on internal anatomy. Relative rate tests suggest that evolution of hemolymph proteins has been about as fast in Hawaii as on continents. Since the absolute rate of evolution of hemolymph proteins in continental flies is known, one can erect an approximate time scale for Hawaiian fly evolution. According to this scale, the Hawaiian fly fauna stems from a colonist that landed on the archipelago about 42 million years ago-i.e., before any of the present islands harboring drosophilines formed. This date fits with the geological history of the archipelago, which has witnessed the sequential rise and erosion of many islands during the past 70 million years. We discuss the bearing of the molecular time scale on views about rates of organismal evolution in the Hawaiian flies.