Mutations in RVS161 and RVS167, the two yeast amphiphysin homologs, cause very similar growth phenotypes, a depolarized actin cytoskeleton, and a defect in the internakization step of endocytosis. Rvs161p and Rvs167p have been shown to interact in the two-hybrid system, but their localization in the cell may be different thus raising the question whether the interaction is physiologically relevant. Here we demonstrate that the two proteins function together in vivo. We find that the steady state level of Rvs167p is strongly reduced in an rvs161Δ strain. Similarly, the level of Rvs161p is strongly reduced in an rvs167Δ strain. We demonstrate that these reduced protein levels at steady state are due to a decreased protein levels at steady state are due to a decreased stability of either Rvs protein in the absence of the other protein. Furthermore, we find that the amount and ratio of Rvs161p and Rvs167p are critical parameters for receptor-mediated endocytosis, In addition, by using the two-hybrid system we show that the interaction of Rvs167p with actin is not abolished in an abp1Δ strain suggesting that Abp1p is not essential for this interaction.