In Y1-xZrxCo3 (0 ≤ x ≤ 0.1) the high field magnetization was observed in pulsed fields up to 40 T at 4.2K, and the transition fields for the itinerant electron metamagnetism were determined in pulsed fields up to 100 T at 10 K. The results show that the itinerant electron metamagnetic transition is induced when the effective field acting on the Co, which is the sum of the applied and the exchange fields, attains the critical value. © 1998 Elsevier Science B.V. All rights reserved.