We have used an irradiation and fusion procedure to generate somatic cell hybrids that maintain fragments of human chromosome 12. To identify hybrids retaining human material we performed repeat element-mediated PCR (intra-ALU PCR) on DNA extracted from individual cell clones. Twenty-five of 38 hybrids tested were shown to contain human material at low passage. These were further characterized by inter-ALU and inter-LI PCR. FISH analysis, using human Cot1 DNA as a probe, revealed the presence of 1-2 fragments in 11 out of 12 hybrids. The majority of the hybrids, 8 out of 12, were found to be homogeneous. The hybrid panel was characterized by 18 markers with known locations covering the entire chromosome 12. Thirteen of the 25 hybrids were positive for at least one marker. The results indicated the following order of loci on 12q: Cen-WNTI-A2MR-RAP1B-D12S8-PTBR-ATP2B1++ +-D12S7-D12S52-IGF1-PAH-PLA2-IFNG-ALDH2-te r. Three hybrids studied in more detail were found to carry overlapping fragments from chromosome segment 12q12-->q14.