Proteins were extracted from styles of 29 self-incompatible cultivars of almond and separated using non-equilibrium pH gradient electro-focusing, and the gels were stained for ribonuclease activity. Mutually incompatible cultivars had similar banding patterns and, for the 24 cultivars already genotyped in France or California, the bands correlated well with the reported alleles. The band corresponding to S-1 of the French labelling system was indistinguishable from that corresponding to S-b Of the Californian labelling system, and a controlled cross confirmed that these alleles are identical. The band corresponding to the Californian S-a, was distinct from the bands corresponding to French alleles and, to harmonise the allele labels, it was redesignated Ss. The genotypes of five uncharacterised self-incompatible cultivars were inferred from zymograms as follows:'Desmayo Largueta' and 'Glorieta', S1S5, 'Masbovera', S1S9, 'Tarragones', S2S9, and 'Tokyo', S6S7 The alleles designated Sg and Ss have not previously been reported. Nine self-compatible cultivars or selections were analysed, and each showed a band corresponding to an incompatibility allele as well as a common band; however, the correspondence of this common band to SS, the allele for self-compatibility, is unproven.