Blood samples from 1,698 unrelated nonLappish Norwegians have been typed in the red cell acid phosphatase system. The allele frequencies found were PA = 0.3807, PB = 0.5601 and PC = 0.0592. Typing was performed also on 196 samples from Norwegian Lapps living in the two communities Kautokeino and Karasjok. The frequencies found were PA = 0.3373, PB = 0.6566, PC = 0.0060 and PA = 0.5664, PB = 0.4248, PC = 0.0088, respectively. The difference in allele distribution between these three population groups was statistically highly significant.