The paper by Ortiz et al. (2004) which concludes that ‘Postcoital administration of levonorgestrel does not interfere with post-fertilization events in the new-world monkey Cebus apella’ has no scientific basis. The conclusions are not supported by the results reported namely in order to demonstrate that after levonorgestrel administration there is a living embryo it is necessary to find cardiac activity in the gestational sac. The authors did not mention cardiac activity in the ultrasound examinations of gestational sacs. Were they living embryos or dead embryos? Dead embryos not yet delivered are ‘missed abortions’ as all obstetricians know. In the human species = 10–15% of clinical pregnancies are aborted spontaneously. Cebus apella monkeys also have spontaneous abortions. In this paper the authors did not mention any spontaneous abortion in cases or controls. Obviously the number of cases is inadequate for a scientific demonstration of the hypothesis: only 24 treatment cycles and 24 control cycles. (excerpt)