Immunoglobulin A-alpha 1 antitrypsin complex (IgA-AT), its constituent components and nine other clinical or laboratory variables were measured in thirty-three patients with early, non-erosive rheumatoid arthritis (RA) in order to assess their value in predicting the subsequent development of erosions. After 12 months, eighteen patients had developed erosions. Comparison of variables measured at outset between the group of patients subsequently developing erosions and those not, showed only the complex IgA-AT level to be significantly different, the mean being higher in the erosive group. In the subgroup of patients with high IgA-AT levels (greater than 3.0 arbitary units) all developed erosions. The possible therapeutic implications of these findings are discussed.