The presence of smooth muscle antibodies (SMA) as determined by indirect immunofluorescence was investigated in the serum of 40 patients, 36 out of which were children. Group I included patients having celiac disease (diagnosed by three biopsies). 7/7 (Group Ia) showed no SMA on gluten-free diet while antibodies were present after challenge. 4/6 (Group Ib) were positive also after challenge (these had not had previous determination). Group II was composed by patients presumed to have celiac disease for they had only one biopsy showing grade IV villous atrophy. 5 patients were of recent diagnosis (group IIa) and showed SMA. 4/5 (Group IIb) who admitted not to had been able to follow the gluten-free diet were also positive for SMA. 6/6 (Group IIc) patients on strict gluten-free diet and showing good clinical response had no detectable SMA. Group III included relatives of patients having celiac disease. 5/6 with SMA showed pathologic small bowel biopsies; only 1/4 with no SMA had mucosal alterations. It is concluded that the presence of serum SMA can be considered a useful marker in the follow-up of cases of celiac disease already diagnosed and to investigate presumed cases of such disease.