It is well known that oestrogen has immunomodulatory properties. We have previously shown disease ameliorating effects of hormone replacement therapy (HRT) in post-menopausal women with rheumatoid arthritis (RA). The aim of this study was to investigate the effects of HRT and the patients inflammatory state on humoral and cell-mediated immune responses. Eighty-eight post-menopausal RA women were allocated to receive HRT (oestradiol and noretisterone acetate), vitamin D3 and calcium or vitamin D3 and calcium alone in a 2-year randomized controlled trial. Immunoglobulins (IgM, IgG and IgA) in serum were measured by nephelometry and rheumatoid factor (RF) concentration by enzyme-linked immunosorbent assay. Immunization with influenza vaccine was performed to quantitate humoral response to recall antigen and tuberculin skin test with purified protein derivative (PPD) to test T-cell-mediated immune response. These immune related measures were correlated with demographic and disease-related variables. HRT during 2 years did not alter concentrations of Ig, RF, IgM response to influenza vaccine or the PPD reaction. The increase in IgM against influenza vaccine was significantly positively correlated with signs of disease activity; C-reactive protein, disease activity score 28 and inversely with haemoglobin. In contrast, PPD reactivity was inversely associated with disease activity. In conclusion, long-term HRT in RA does not influence Ig or autoantibody concentrations in serum and has no significant impact on humoral and cell-mediated immune responses to recall antigens. Interestingly, high disease activity was associated to increased humoral but decreased cell-mediated immune responses irrespectively of hormone treatment.