We investigated whether fetal DNA from the maternal blood can be used to diagnose abnormalities of chromosomes 13, 16, 18 and 21 in spontaneous miscarriage. Venous blood was obtained from 50 women with a diagnosis of spontaneous miscarriage. The evacuated products of the uterus were also sampled. DNA was extracted from both blood and tissue samples. Polymerase chain reaction (PCR) was performed using microsatellite markers for selected chromosomes. A novel technique using a capillary sequencer was employed. The electrophoretogram created was analysed using GeneScan software. The result obtained from the maternal blood samples was compared to the result obtained from uterine samples. Forty-two of the 50 (84%) cases were found to have a trisomy of one or more of the chromosomes tested on analysis of maternal blood. Compared to the overall result obtained on the uterine products of conception, the sensitivity was 97.6 and specificity 1.0. Trisomy 16 was the most common abnormality detected. These results suggest that the incidence of genetic abnormalities complicating miscarriage may be higher than suspected hitherto.