The cell-envelope proteinase from Lactobacillus helveticus CRL 1062 was detected in the cell membrane fraction. The enzyme remained associated with the cells even after treatment with lysozyme and was not released from washed cells in absence of calcium. The proteinase was maximally active at pH 6.5-7.0 and 42 degrees C and hydrolysed alpha- and beta-caseins at different rates. Activity was inhibited (98%) by 1 mM PMSF, suggesting it was a serine-type protease.