The productivity of stable Chinese hamster ovary cell lines secreting HIV-1 monomeric (IIIB gp120) and oligomeric (UG21 gp140) recombinant envelope glycoproteins was compared in serum-containing (S+), serum-free (S-) and protein-free (P-) culture media. UG21 gp140 expression was greatest in S+ medium, while IIIBgp120 production was lower than gp140 in all three media but highest in S-. UG21 gp140 production was highest in standard 850-cm(2) roller bottle cultures in S+ media, peaking after 14 days of incubation, while expression levels in the three media were 0.5 (S+), 0.4 (S-) and 0.2 (P-) mg/l, from which 90, 80 and 12% of gp140, respectively, could be purified by immunoaffinity chromatography. Purified UG21 gp140 from S+ and S- media possessed biological functionality as evidenced by CD4 and monoclonal antibody (Mab) binding. In contrast, UG21 gp140 from P- medium appears to be misfolded and non-functional. Despite the possession of a different N-linked glycan profile, UG21 gp140 from S- media shows very similar CD4 and Mab binding characteristics to S+ UG21 gp140. The relevance of these findings to HIV vaccine development is discussed.