Interferon (IFN) therapy is currently not approved for use during pregnancy. Two HIV-seropositive pregnant women, who were due to undergo abortion in the second trimester of pregnancy, were given a single intramuscular dose of IFN-α, with their informed consent. Blood samples were taken simultaneously from the mothers and fetuses, together with amniotic fluid. IFN was undetectable in the fetal blood and amniotic fluid in both cases. Pharmacokinetic parameters were similar to those in nonpregnant women. We conclude that maternal IFN-α during pregnancy should be safe for the fetus. The indications for IFN therapy in pregnancy could therefore be the same as those in the non-pregnant stat