The effect of African swine fever (ASF) virus infection on reproductive performance of recovered sows and their pigs was investigated. Six sows were inoculated with a 1979 ASF isolate from the Dominican Republic. One sow was bred on postinoculation day (PID) 58 and killed on PID 148. Four sows were bred between PID 368 and 419 and were allowed to farrow. One sow did not conceive. Samples collected during pregnancy, at farrowing, and during lactation were tested for virus by tissue culture and animal inoculations to determine whether ASF virus recrudesced during these natural stresses. Virus was recovered only from tissues of the sow killed on PID 148. Virus was not detected in tissue samples from the 4 other sows or from any fetus or neonate. Sow and neonatal pig sera, colostral whey, and milk whey were assayed for antibodies against ASF viral antigens, using an enzyme-linked immunosorbent assay. Antibody values in sows' sera did not change appreciably during pregnancy, farrowing, or lactation. One litter of pigs was raised with their sow. Weekly serum samples were tested for passively acquired antibodies. At 7 weeks of age, the litter was challenge inoculated with the same virus as that used initially to infect their dam. Viremia titers, duration of viremias, and clinical course were reduced. One young pig did not develop fever, viremia, clinical disease, or antibody response to virus challenge exposure. The altered course of infection was attributed to protective effect of passively acquired antibodies.