The nimA gene encodes a protein-serine/threonine kinase that is required along with the p34cdc2 kinase for mitosis in Aspergillus nidulans. We have searched for human protein kinases that are related to the NIMA protein kinase using the polymerase chain reaction. Different pairs of degenerate oligonucleotides specific for conserved amino acid motifs in the catalytic domain of NIMA were used as primers in the polymerase chain reaction to amplify partial complementary DNAs (cDNAs) of protein kinases expressed in the promyelocytic leukemia cell line HL-60. Forty-one distinct cDNAs representing a broad spectrum of serine/threonine- and tyrosine-specific protein kinases were identified, and the sequences for 21 of these protein kinases were found to be unique. Three of these cDNAs represent a family of protein kinases whose members are related to NIMA and the murine nimA-related protein kinase Nek1. We discuss the success of this polymerase chain reaction approach with respect to the use of multiple primer pairs, the influence of primer degeneracy, and the tolerance of cDNA amplification to mismatches between primers and template mRNA.