1. A subcutaneous injection of hydroxyindoleacetic acid (HIAA), melatonin (MEL), methoxytryptophol (MTP) or methoxytryptamine (MTA) (1 mg/25 g body wt/injection) at 8.5 days post-coitum (p.c.) did not produce any effect on the development of embryos in utero at 10.5 days p.c. 2. Two subcutaneous injections (3 mg/25 g body wt/injection) of MTP, but not HIAA, MEL nor MTP, at 7.5 and 8.5 days p.c. brought about a decrease in gravid uterine weight and number of live fetuses and an increased incidence of early resorptions at 17.5 days p.c. 3. MEL at doses 100 and 200 mu g/ml, MTP at doses 50 and 100 mu g/ml and MTA at 25, 50 and 100 mu g/ml brought about an increase in the number of abnormal embryos cultured in vitro and an increased incidence of abnormal yolk sac circulation, body axis, optic and otic placodes, branchial apparatus, forelimb buds and cranial neural tube. 4. The findings show that melatonin, methoxytryptamine and methoxytryptophol produced an embryotoxic effect on embryos at the early somite stage in vitro while only methoxytryptamine had an adverse effect on embryonic development in vivo.
