Tests for a dysimmune state were done in an unselected group of 67 patients with agnogenic myeloid metaplasia (AMM). The results were compared to those of 56 patients with polycythaemia vera (PV). 75% of AMM patients versus 32% of PV patients had various abnormalities. The most frequent disorders among AMM patients were serum antinuclear and anti smooth muscle autoantibodies (10.3% each), a positive test for rheumatoid factor (21.7%), a polyclonal increase in serum immunoglobulin levels (46.8%) or a serum monoclonal component (9.7%), a positive direct Coombs' test (19%), an anti I autoantibody (30%). In AMM patients there was no relationship between age, sex, importance of splenic enlargement, time from diagnosis or treatment and the present of a dysimmunity. Furthermore, in AMM patients, but also in PV patients, it seems that the more frequent and numerous these abnormalities the more severe is the myelofibrosis. Like other previous studies, these results suggest a lymphoid cell involvement in AMM and a role for these immune disorders in the pathogenesis of myelofibrosis.