Two lines of evidence suggest that amino acid transport systems and the methylamine/ammonia transport system of Saccharomyces cerevisiae may share a common component or components. 1. Mutant strains have been derived which are defective in transport activity for methylamine and for amino acids. A single pleiotropic mutation appears to be responsible for the observed reduction in the various transport activities. 2. Transport systems for amino acids and for methylamine are sensitive to a similar degree to inhibition by proton conducting uncouplers, ATPase inhibitors, and ionophores.