The multiallelic mating type locus B alpha 1 of Schizophyllum commune encodes a pheromone receptor and putative pheromone genes. A comparison of two alleles encoding receptors that share the same specificity B alpha 1 was performed using strains of different geographic origin. The amino acid sequence alignment revealed strong conservation of the largest part of the receptor. Only in the distal C-terminus major amino acid was divergence encountered. This C-terminal region of 117 of the total of 639 amino acids was shown to be unnecessary for function in vivo by transformation experiments.