The levels of murine leukaemia virus (MuLV) proteins p30 and gp70, antinuclear antibody (ANA), anti-soluble nuclear protein, anti-single-stranded DNA, anti-double-stranded DNA and anti-histone antibodies were measured in B10.A and B10.A recombinant mice neonatally infected with MuLV-Scripps (Lerner et al., 1972). The incidence and latency of lymphoma and the incidence of glomerulonephritis were also determined. The mice studied could be divided into high-responder and low-responder groups. Most of the high ANA antibody could be attributed to anti-histone antibody. High response was associated with the H-2b haplotype and recombinant strains on the B10 background which were identical at the I-A subregion derived from the H-2b parental stock. In contrast, low ANA response was associated with the I-A subregion derived from the H-2k haplotype. In all groups of virus-inoculated animals, most animals developed serum elevations of p30 and gp70 and at least 72% of the inoculated animals developed lymphomas. High serum p30 levels correlated inversely with latency and directly with gp70 values. From 4 to 28% of the animals in each virus-inoculated group had histological evidence of glomerulonephritis, although no clear genetic basis could be ascribed to the incidence of glomerulonephritis, serum p30 or gp70 levels, or latency of lymphoma development.