BACKGROUND: Rheumatoid arthritis (RA) is an autoimmune disease with progressive activity. The RA remission was observed in women during pregnancy, but the mechanism responsible for remission is hypothetical only and concerns mechanisms of immune regulation such as lymphocyte subpopulations and interleukin production. AIMS: The lymphocyte subpopulations and interleukin production in vitro in a group of healthy non-pregnant women, healthy pregnant women and pregnant women suffering from RA may help towards a better understanding of regulation of the immune processes. METHODS: The investigations were performed in trimester III--2 days after delivery and 6 weeks after delivery. Peripheral blood lymphocytes were isolated on Gradisol gradient and analysed immediately or after having been cultured for 72 hours in RPMI medium supplemented with 10% FCS. The cultures were terminated after 72 h, supernatants stored at -72 degrees C for interleukin evaluation. The concentrations of IFN-gamma, IL-2, IL-6, IL-12, TNF-alpha and its soluble receptors R-I, R-II were estimated in non-stimulated and PHA (Sigma, 5 microg/ml) stimulated culture supernatants using ELISA Endogen kits according to the manufacturer's instructions. RESULTS: The general pattern of T cell subpopulation distribution was similar in all analysed groups. Decreased IFN-gamma, IL-12 and increased IL-6 production by lymphocytes after PHA stimulation was found in trimester III in pregnant women with RA as compared to healthy pregnant woman. CONCLUSION: The obtained results suggest that in pregnant women with RA the TH1 cell response predominates, contrary to healthy pregnant women with TH2 type functional response. These phenomena were not observed after delivery.