Two groups of intermediate-to high-grade non-Hodgkin's lymphoma patients aged 65 years and over were enrolled in a dose-range study of CHOP therapy utilizing 5 doses (1/2, 7/12, 2/3, 5/6, full CHOP): 11 patients 65-79 years of age (group A) and 9 patients 80 years or older (group B). The patients were enrolled consecutively; the study was designed so that if 3 patients completed 3 cycles of CHOP on schedule without major problems, the next highest dose was administered. If 2 patients experienced any major problems during 6 cycles at a given dose, treatment was discontinued and the dose prior to that particular dose was regarded as the optimal dose. The 6 treatment cycles were completed by 3 of 3 (2/3 CHOP), 3 of 4 (5/6 CHOP), and 1 of 4 (full CHOP) group A patients; and by 3 of 3 (1/2 CHOP), 2 of 3 (7/12 CHOP) and 1 of 3 (2/3 CHOP) group B patients. The results indicated that the optimal doses for group A and B were five-sixths and seven-twelfths of the standard CHOP dose, respectively.