The nuclear DNA content of 55 ectopic tubal pregnancies was studied by flow cytometry from paraffin embedded tissue blocks. An abnormal amount of DNA content was found in 24% of the cases. This was a significantly higher percentage than encountered in 92 spontaneous abortions studied by the same method in the same population (8%, P=0.01). The result indicates that, in addition to the maternal factors, abnormal embryogenesis with grave chromosomal aberrations may play a major role in the etiology of ectopic pregnancy.