Lymphocyte function-associated antigen 1 (LFA-1) was immunoprecipitated from various types of surface-radioiodinated murine lymphocytes, and analyzed by two-dimensional polyacrylamide gel electrophoresis. LFA-1 alpha and beta chains from splenic B lymphocytes had the same apparent molecular weights as, but distinct isoelectrofocusing patterns from, their counterparts from thymocytes or splenic T lymphocytes. The splenic B lymphocytes lacked a basically charged population of alpha chain, while the thymocytes and the splenic T lymphocytes showed both the acidic and the basic portions. Furthermore, the beta chain of the former migrated more towards the acidic end than that of the latter. No difference was found between LFA-1 molecules of the same lineage of cells from several strains of mice whose H-2 haplotypes were different from one another. When murine lymphocyte lines were examined, LFA-1 with various isoelectrofocusing patterns were recognized. The charge difference again reflected the difference in lymphocyte lineage, but in a more exaggerated manner than that seen with cells from mice. The average acidity of both chains of LFA-1 decreased in the order of B cell lines, pre-B cell lines and T cell lines. The lineage-dependent charge difference of either chain disappeared after neuraminidase treatment of LFA-1, indicating that lymphocyte differentiation was accompanied by changes in LFA-1 sialylation.