Genomic DNA from 60 cases of acute myeloid leukaemia (AML) was screened for mutations in the c-kit gene. DNA from all 21 exons was subjected to polymerase chain reaction (PCR) amplification and analysis by conformation sensitive gel electrophoresis (CSGE); exons showing altered CSGE patterns were then sequenced. Mutations were identified only in those patients with inv(16) (3/7 cases) or t(8;21) (1/2 cases) and comprised three in-frame deletion plus insertion mutations (exon 8) and one point mutation (exon 10, GTA --> ATA, Val530Ile). Exons 8 and 10 were then analysed in 31 further cases of inv(16) (n = 14) and t(8;21) (n = 17), revealing four additional exon 8 in-frame deletion plus insertion mutations, all of which were in cases of inv(16). All exon 8 in-frame deletion plus insertion mutations (n = 7) involved the loss or replacement of the codon for Asp419 which is highly conserved cross species and is located in the receptor's extracellular domain. The high frequency of the c-kit proto-oncogene exon 8 deletion plus insertion mutations in AML suggests an essential role for this region of the receptor's extracellular domain. The association with inv(16) invites speculation as to the link between these two changes in the pathogenesis of AML.