We have conducted a study on the spontaneous and UV-A-induced frequency of chromosomal breaks and sister-chromatid exchanges (SCE) in purified lymphocytes from normal donors and from systemic lupus erythematosus (SLE) patients who were in clinical remission at the time of the study. Our results show that although SLE lymphocytes exhibit a higher frequency of spontaneous SCEs than controls, the rate of chromosomal breakage is comparable in the 2 groups. In both controls and patients, irradiation with UV-A (320-400 nm) increases the SCE values but does not significantly affect the frequency of chromosomal aberrations.