SummaryA partial swine cDNA which encodes the functional domain of PIT‐1 was isolated by the polymerse chain reaction (PCR). The swine PIT‐1 cDNA clone is 95% identical at the protein level to the rat Pit‐1 gene. Thus, Pit‐l's known function in control of rat growth hormone and prolactin expression is likely to be conserved in swine. This swine cDNA clone was used to investigate genetic variability at PIT‐1 in several American and Chinese breeds. PolymorphicBamIII fragments were found in pure‐bred Meishan animals (n= 13), but only monomorphic fragments in five American bre