We have characterized a truncated secreted form of the HIV-1 envelope glycoprotein gene. Expression via a recombinant vaccinia virus resulted in a glycoprotein product of approximately 140 kDa (gp160t) and a minor cleavage product of 120 kDa (gp120). Pulse-chase analysis revealed that the majority of gp160t remained cell-associated and underwent degradation within 10-20 hr of synthesis. A secreted form (gp160t/sec) and gp120 were detected in the media 2-4 hr postsynthesis and were not significantly degraded within a period of 20 hr. Most of the cell-associated gp160t remained sensitive to digestion with endoglycosidase H, whereas gp160t/sec and gp120 were largely resistant. Gp160t, gp160t/sec, and gp120 formed oligomers which were stabilized by intermolecular disulfide bonds and/or noncovalent interactions and were also found to bind to soluble CD4. Both wild type gp160 and wild type gp160t were observed to undergo a post-translational modification 4-5 hr postsynthesis, resulting in glycoproteins with a slightly increased electrophoretic mobility. These differences in electrophoretic mobility remained following treatment with N-glycosidase F, indicating that they are not a consequence of N-linked oligosaccharide processing, but may represent an additional modification of the envelope glycoprotein.