Lactoperoxidase catalysed 125I-iodination of cerebellar interneurone enriched cultures grown in serum-supplemented or in serum-free, chemically defined medium was studied. It was observed that the differences in the adhesion properties of nerve cells under these conditions are accompanied by differences both in the degree of 125I-iodination of the proteins on the plasma membrane of nerve cells and in the profile of the labelled polypeptides resolved by SDS-polyacrylamide gel electrophoresis. The relative labelling of the major 125I-iodinated polypeptides changed with time in both types of cultures, suggesting that alterations in the overall organisation of the neuronal plasma membrane occur during the development of the cells under both culture conditions. The developmental changes affecting the D2 protein (which is nerve cell specific in these cultures) were significantly retarded in the neuronal cultures grown in the serum-free medium compared with those grown in the serum-containing medium: the increase in D2 content was reduced by 7 DIV and the maturational change in the molecular form of D2 was retarded significantly during the whole cultivation period. The degree of surface 125I-iodination of cerebellar astrocytes in culture was only a fraction (7-20% depending on cultivation time and conditions) of that of the neuronal cultures and the labelled polypeptide profiles obtained from the two types of cultures were markedly different. In comparison with cultures in the serum-supplemented medium, astrocytes under the serum-free conditions showed only minor and transient differences in the profile of surface 125I-iodinated proteins, although the morphology of the cells was markedly different.