Type II and III CD4⁺ clones were examined for their degrees of proliferation in response to stimulation with various allogeneic PBLs. Responder clones (5 × 10⁴ cells) were cultured with 30 Gy irradiated allogeneic PBLs (1 × 10⁵ cells). After 24 hours of culture, 1 μCi of ³H-thymidine was added periodically to each well while incubation was continued for another 18 hours at 37°C. The rate of uptake of ³H-thymidine (cpm) into high–molecular-weight DNA was determined using a liquid scintillation counter. Stimulators: (1) responder alone; (2) A*2402,3303, B*4403,5401, DRB1*0405,1302; (3) A*2402,2602, B*5201,4002, DRB1*1405,0901; (4) A*2402,3303, B*5201,4403, DRB1*1406,1502.