We describe a heteroduplex analysis for the detection of the 185delAG mutation in the BRCA1 gene. The protein truncation test (PTT) has previously been used to identify many of the mutations in BRCA1 that result in premature termination of the protein. However, we were not able to detect the 185delAG mutation by PTT and suggest that heteroduplex analysis may complement PTT for analysis of BRCA1 mutations. This simple technique may be useful for studies on the prevalence and the penetrance of the 185delAG mutation.