The significance of abnormal serum anti-DNA and complement levels persisting in SLE patients on treatment has been explored. Instances when serologic abnormalities returned to normal were followed by a significantly longer mean duration of remission. When anti-DNA persisted at abnormal levels, a more severe exacerbation was likely to follow, although this result was not the case for persisting hypocomplementemia. These data did not result from two variants of SLE, one mild and one severe, because druation of remission correlated directly with dosage of steroid. Randomly discovered abnormalities in anti-DNA and complement levels were of limited predictive value, because they frequently persisted for over 1 year before exacerbations occurred. Hypocomplementemia resolved spontaneously without recognizable exacerbation in nearly half the observed instances.