High-affinity rosette-forming T-cell assays were performed by incubation of peripheral-blood mononuclear cells with sheep erythrocytes (E) at 29 degrees C. As compared with normal controls, the levels of high-affinity rosette-forming cells (RFC) were much more frequently depressed in cancer patients than were the total E-RFC incubated at 4 degrees C. Only 2/83 normal controls had less than 38% 29 degrees C E-RFC (mean 48 +/- 5), whilst 78/89 cancer patients were below this level. The few postoperative patients tested exhibited a normal range of 29 degrees C E-RFC. The 29 degrees C E-rosette assay gives reproducible counts of a T-cell subset, and is a sensitive assay for evaluating the immune status of cancer patients.