In this study we quantified the transmission of pseudorabies virus (PRV) in well-immunized sow herds in The Netherlands. In three herds, sows were tested for antibodies to gE of PRV every time after they had been transported to another barn (survey A). In 99 other herds, sows were tested simultaneously once or twice yearly (survey B). We observed six introductions in survey A and 53 in survey B. None of these introductions resulted in extensive spread of the virus. The reproduction ratio R, which is defined as the mean number of secondary infections caused by one infectious sow, was significantly less than one. We conclude that PRV can be eliminated from sow herds by vaccination.