The chromosomal localisation of the human gene coding for peroxisomal 3-oxoacyl-CoA thiolase (ACAA) was determined by human-hamster somatic cell hybrids and fluorescence in situ hybridisation, using cDNA and genomic probes, respectively. The results allowed an exclusion of the previously suggested presence of a second site for ACAA on chromosome 11 and an assignment of the gene to a single chromosome band (3p22).