A PC-based image analysis system for gel photographs of DNA gel patterns was developed. It was originally designed as a general-purpose, low-cost, yet high-performance system for wide applications in the biomedical area. In this study, we performed analysis of gel images obtained by polymerase chain reaction (PCR) amplification. The system employs a high-resolution CCD camera that can accurately measure grayness of the gel photographs for quantitative analysis of PCR products. The target DNA (exon 52 of the dystrophin gene), which had been found to be deleted in some patients with Duchenne/Becker muscular dystrophy (DMD/BMD), was amplified for the female family members together with the control DNA (exon 60) as a reference. The ratio of the target DNA to the control DNA was determined from PCR products to identify the carrier status of this disease by means of gene dosage. We conclude that 'the PC-based image analysis system' was useful for quantitative deletion analysis of DMD/BMD heterozygotes.