Abstract A series of diploid plum (Prunus salicina Lindl. and hybrids), apricot (P. armeniaca L.), and plum × apricot (plumcot) clones were surveyed for six enzyme systems to identify a biochemical marker system for plumcots. Peroxidase (EC 1.11,1.7) was the best marker for identifying plum × apricot hybrids. The other systems contained plum or apricot specific alleles useful in verifying hybrid parentage of first or later generation derivatives.