The structure and expression of the HTLV-1 envelope protein was examined using T lymphoid cell lines infected with HTLV-1 and recombinant vaccinia viruses expressing the HTLV-1 envelope. Pulse-chase experiments demonstrated that the envelope precursor, gp62, had a half-life of 7-12 hr. N- glycosylation of the precursor protein was examined using tunicamycin and endoglycosidase H. These studies revealed that at least four and possibly five potential N-glycosylation sites were utilized. In addition, the envelope precursor was found to sediment on sucrose gradients as high-molecular- weight complexes, in positions consistent with the formation of dimers and smaller amounts of higher multimeric forms. Finally, the recombinant vaccinia system was used to express mutants designed to analyze the role in HTLV-1 envelope processing of the cytoplasmic tail and the membrane-spanning domain.