Data represent the number of colonies of donor type by PCR over the number of colonies of each type tested. A colony from which the male-specific sequence did not amplify was defined as negative only if the DNA sample was considered intact or not degraded as determined by the ability to amplify a 300-bp β2-microglobulin sequence from the sample. A sample from which we failed to amplify both the male and β2-microglobulin products was defined as nonevaluable and was not included in the analysis. Of a total of 63 male-negative colonies, 46 (73%) had intact DNA as judged by PCR for the β2-microglobulin sequence. More than half of the samples that had degraded DNA had been stored at −70°C for more than 18 months.