1. Three cases of acute rejection were detected by macrophage migration inhibition tests (MIT) conducted directly on seven patients who had received renal allografts. The macrophage migration inhibitory factor (MIF) activity was positive in all cases 1-2 days before the appearance of acute rejection. 2. After the administration of a high dose of Solu-Medrol (1g/day for 3 days) to suppress the acute rejection, MIF activity recovered to its normal level 3 days later. These findings seem to indicate that MIT yields immunologically useful criteria for the early detection of an acute rejection.</p
