A capture enzyme immuno assay for the detection in the serum of specific IgA antibodies to HAV is described. A total of 203 sera from patients and controls were tested. IgA anti-HAV were present only in sera from patients with recent hepatitis A. 23 patients were followed prospectively and IgA anti-HAV were at detectable levels for at least six months after the onset. The detection of IgA anti-HAV is proposed as an important test to differentiate hepatitis A with persistent hypertransaminasemia from non-A, non-B patients.