The purpose of this study was to determine whether in vivo changes in the repertoire of Tcr beta chain variable region (V beta) genes could be detected in peripheral blood mononuclear cells after immunization of humans with recombinant hepatitis B virus envelope protein (rHBsAg). We measured the percentage of Tcr RNA transcripts carrying each of 20 V beta genes in human PBMC before and after immunization with rHBsAg in Polynesians (8 non-immunized controls, 26 immunized subjects) and Europeans (9 non-immunized controls, 11 immunized subjects). The per cent of RNA transcripts containing V beta 7.4 family genes was increased in immunized vs control Polynesian (+ 1.6 +/- 0.5%) vs -1.1 +/- 0.3%, P = 0.0002) and European (+1.6 +/- 0.6% vs -0.1 +/- 0.5%, P = 0.05) subjects at 48 h and 28 h post-immunization, respectively. No changes in V beta repertoire were found after 48 h in either race. Thus, there is a transient increase in frequency of T cells with Tcr containing V beta 7.4 family genes within 48 h of an immunization containing rHBsAg in humans. There are a number of explanations for this finding, including the possibility that V beta 7.4 gene family products may be preferentially involved in the primary immune response to HBsAg.