Genetic polymorphism of serum albumin was demonstrated by isoelectric focusing in wild rabbit populations from Portugal and England. Gene frequencies were estimated to be (1)ALB.I = 0-47, ALB*2 = 0*49,ALB*3 = 0.04, in Portugal, and (2) ALB*l = 0-60 and ALB*2 = 0-40, in England. One hundred Portuguese domestic rabbits of mixed breeds were all of ALB I type.