Embryo prostaglandin (PG) synthesis plays a role in the modulation of embryo metabolism and viability, and in the beginning of the implantation. The effects of ethanol consumption seem to be mediated at least in part by PGs. Increased PG production of postimplantation embryos is associated with retardation and abnormalities in the gestational period. The aim of this study was to find out the effects of low chronic ethanol ingestion by mice, previous to pregnancy, on the PGE released by in vitro and in vivo derived embryos. Immature females or adult males were treated with 5% ethanol for 30 days. After fertilization and mating, two-cell embryos, morulae and blastocysts were collected. The PGE synthesis and release were measured by radioimmunoassay. PGE production by in vitro derived two-cell embryos from ethanol-treated females was lower than in the control group (P < 0.01). Also, PGE production was reduced when two-cell embryos came from ethanol-treated males (P < 0.01). There were no differences in PGE synthesis by in vitro derived morulae and blastocysts in these groups. Two-cell embryos derived from mating produced lower quantities of PGE when they came from ethanol-treated females mated with control males, as compared to the control group. PGE release by in vivo derived blastocysts from ethanol-treated females was reduced significantly, as compared to the control group (P < 0.01). We conclude that a low concentration of ethanol administered chronically to immature females reduces PGE synthesis and release by two-cell embryos from culture in vitro, and by embryos of days 2 and 4 from in vivo development.