The relationship between autoantibody reactivities and nephritis in systemic lupus erythematosus (SLE) is unclear. We studied MRL/l mice which developed a considerable albuminuria (either mice with short ( < 1 week) or heavy and prolonged (3 weeks) albuminuria) and compared them with non-albuminuric age-matched controls, with young (12 weeks old) non-albuminuric mice and with mice which were followed for 36 weeks and did not develop albuminuria. In a longitudinal prospective study on plasma samples we correlated a variety of anti-nuclear reactivities and reactivities against extracellular matrix (ECM) components, with the onset of albuminuria. We found that at the onset of albuminuria, anti-DNA was higher while anti-nucleosome and anti-H2A/H2B-DNA subnucleosome reactivities were lower compared with age-matched non-albuminuric mice. We also studied glomerular eluates of these mice in ELISA and in indirect immunofluorescence (IF). In the eluates we found with IF that anti-glomerular basement membrane (GBM)-tubular basement membrane (TBM) antibodies were already present in 12-week-old non-albuminuric mice. These eluates showed no anti-nuclear antibodies. In eluates of albuminuric mice more immunoglobulin was deposited, and anti-ECM, anti-DNA and anti-nucleosome reactivities were higher than in eluates of age-matched non-albuminuric mice. The deposition of anti-nucleosome antibodies preceded the deposition of anti-DNA antibodies since they were deposited to a greater extent in mice with a short albuminuria. We conclude that anti-GBM-TBM antibodies are the first autoantibodies that deposit in glomeruli of MRL/l mice at an early age. The onset of albuminuria is associated with additional deposition of both anti-ECM and anti-nuclear (anti-nucleosome and anti-DNA) antibodies, but the difference with non-albuminuric mice seems to be more quantitative than qualitative.