The mutant JV66 was selected from the wild type strain of S. pombe 972h- ade7-413 by its ability to grow on solid rich medium containing 200 micrograms Dio-9/ml. The single nuclear mutation, designated pma1 gives resistance towards diguanidines and several other positively charged compounds. The pma1 mutation also decreases plasma membrane ATPase activity and confers resistance of ATPase to vanadate. The pma1 locus is localized on chromosome I at 5.3 map units from cyh1-C7 and at about 20.7 map units from the centromere. This new mutation is genetically and phenotypically different from the mutation cyh3 and cyh4 previously described (Johnston and Coddington 1983).