To the Editor: The report of Donadio and his associates on the treatment of diffuse proliferative lupus nephritis1 contains a point of confusion centering on the use of the terms “clinical flare-up” (or “recurrence”) and “progression” and the implications of this usage regarding the temporary or permanent nature of the observed clinical phenomena. A clinical flare-up, as defined, has no requirement for permanent deterioration, and indeed 84 per cent of patients with such a flareup defined at entry into the study showed subsequent improvement at six-month follow-up examination. In contrast, “progression“ is used in the context of continuing deterioration … progression. © 1979, Massachusetts Medical Society. All rights reserved.