Production of transgenic domestic animals by microinjection of egg nuclei has permitted the introduction of exogenous genes into the transgenic animal. Pursell et al (1) report severe synovitis, cardiomegaly, dermatitis, renal disease and gastric ulcers in pigs with an expressed bovine growth hormone transgene. I have hypothesized that rheumatoid arthritis (RA) is a disease with initial symptoms to the gamete (2, 3). This hypothesis is supported by data showing a reduced rate of RA in women using oral contraceptives (4, 5) and remission of RA in pregnancy (6). RA in animals resulting from trauma to the gamete would be consistent with this hypothesis. This paper hypothesizes that some of the pathology associated with genetic engineering of livestock can be attributed to a rheumatoid arthritis-like spectrum of symptoms. This systemic reaction could be sufficiently similar to human RA to permit the transgenic pig to serve as an animal model of the disease.