Studies of the mechanism of protein secretion in a Gram-positive bacterium, Bacillus subtilis, yielded results very similar to those previously obtained with a Gram-negative organism: nascent chains protruding from protoplasts could be labeled extracellularly; the labeled chains could be recovered on polysomes isolated from the membrane--polysome fraction; they could be released by puromycin, low Mg2+, or chain completion; the completed chains include a known secreted protein (alpha-amylase); and their ribosomes appear to be attached to membrane solely by their nascent chains. The reagent used for extracellular labeling, [1252]diazoiodosulfanilic acid, yielded severalfold more specific labeling of the nascent chains (7--10% of the total cellular labeling and one-fourth to one-third of that of the membrane--polysome fraction) than was obtained earlier with another nonpenetrating reagent.