Generation of an effective vaccine against human immunodeficiency virus type 1 (HIV-1) must overcome problems associated with extensive genetic diversity. Although we previously reported vaccine-induced protection of chimpanzees against infection with an HIV-1 strain different from the one used to make the immunogens, both the HIV-1 vaccine and challenge strains were classified within subtype B. To determine whether the HIV-1-specific immunity elicited might also prevent infection by a strain of HIV-1 from a different clade, the same chimpanzees were given booster inoculations with the rgp160-MN/LAI (recombinant hybrid gp160 molecule) and V3-MN immunogens and then were challenged by intravenous inoculation of a comparable dose of a subtype E HIV-1 from the Central African Republic. Both animals became infected with the subtype E virus, indicating that intraclade vaccine-mediated protection does not predict interclade protection, at least in the context of intravenous challenge and the HIV-1 strains used. This study has important implications for planned phase III efficacy trials of similar vaccine preparations in Thailand where HIV-1 subtype B and E strains cocirculate.