The effect of pregnancy on the incidence and severity of pristane-induced arthritis was examined along with the glycosylation status of IgG during the ante-natal and post-partum periods. It was found that pristane-induced arthritis is prevented by pregnancy. In addition, the levels of agalactosyl IgG fall during pregnancy but rise to greater than normal within a few days of parturition, before resetting towards the norm shortly afterwards. Interestingly, the level of agalactosyl IgG correlates with the severity of arthritis. As previously reported IL-6 may be an important factor, not necessarily the only one, in the production of agalactosyl IgG. Here it is clearly demonstrated that the kinetics of IL-6 activity post-pristane injection parallels the kinetics of agalactosyl IgG production. In addition, the overshoot in agalactosyl IgG levels immediately post-partum coincides with a burst in IL-6 activity. It is considered that these changes in IgG glycoform levels, or the factors which control them, may be related to the mechanisms underlying prevention/remission of arthritis during pregnancy.