During the course of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), several immune and neuroendocrine changes associated with pregnancy may exert positive (amelioration) or negative (exacerbation) effects on the clinical outcome. In order to shed light on the mechanisms underlying these responses, we performed a prospective longitudinal study in RA and SLE pregnant women, including healthy pregnant women as a control group. Cytokine messenger RNA (mRNA) expression assessed by quantitative competitive polymerase chain reaction (PCR) in peripheral blood mononuclear cells (PBMC), cytokine levels and lymphocyte proliferation responses (LPR) following phytohaemagglutinin (PHA) stimulation of PBMC, plasma metalloprotease-9 activity (MMP-9) and hormonal status during pregnancy were determined. TNFa was the most abundant cytokine mRNA expressed in PBMC in all groups studied (healthy pregnant women, RA and SLE pregnant patients). However, a general TH2 response reflected by high IL-10 levels was found in RA, as well as SLE, patients. A significant change in IFN-gamma was observed in RA patients but only during the first trimester of pregnancy. This compared with a major TH1 response in healthy pregnant women. Interestingly, our study showed a homogeneous hormonal pattern in RA and SLE patients. Although decreased cortisol levels were observed in all patients studied, this is possibly related to the remission of disease activity status brought about by steroid treatment before and during pregnancy. In summary, we suggest that complex immune and hormonal networks are involved in pregnancy and that rheumatic diseases are very dynamic immune processes that cannot be described with a clear-cut cytokine profile. Furthermore, the observations in this study may reflect treatment-related immune effects more than those associated with disease.