A possible association between alpha 2-pregnancy-associated globulin (alpha 2-PAG) and activity of rheumatoid arthritis (RA) during pregnancy was investigated. In a prospective study, the correlation between disease activity and serum alpha 2-PAG levels during and after pregnancy was evaluated in 11 women with RA. For comparison, 12 women with ankylosing spondylitis (AS) and 14 healthy women were also studied. No correlation between improvement of disease activity and serum alpha 2-PAG levels could be detected in pregnant RA or AS patients. In contrast, a positive association between total disease activity score and serum alpha 2-PAG levels was found in pregnant RA and AS patients.