To elucidate whether T-cell receptor Jbeta gene usage was affected by major histocompatibility complex haplotypes and other genetic backgrounds, we investigated such usage with Jbeta-specific probes in four different mouse strains. As a result, (a) frequent usage of Jbeta2.1 and Jbeta2.6, (b) infrequent usage of Jbeta1.3, Jbeta1.5 and Jbeta1.6, and (c) predominant usage of the Jbeta2 cluster compared to the Jbeta1 cluster were found. Importantly, these biases were common to almost all the tested Vbeta families of the four strains. Thus, TCR Jbeta usage would be independent of the major histocompatibility complex haplotypes and other genetic backgrounds.