AbstractWe have the substructure and polypeptide composition of the peroxisomal membranes in two methylotrophic yeasts in relation to different growth conditions. The results obtained that no significant ultrastructural differences existed between the membranes of variously grown cells.The presence of specific peroxisomal membrane proteins (PMPs) was studied biochemically. On sodium dodecyl sulphate‐polyacrylamide gels of purified microbody membranes isolated from methanol‐grownHansenula polymorpha, prominent proteins bands were observed at 22, 31, 35, 42, 49 and 51 kD. These proteins were also present when the cells were grown in media containing ethanol and/or ethylamine. Apart from these, several other PMPs were specifically induced under these conditions, namely 24, 29, 37 and 62 kD proteins. The polypeptide composition of peroxisomal membranes fromH. polymorphawas compared with that of another methylotroph.Candida biodinii. In the latter organism a specific PMP with a molecular weight of 23 kD was induced during growth onD‐alanine instead of ammonium sulphate as the nitrogen s