58 fecal specimens from 14 patients (10 hepatitis A, 2 hepatitis B and 2 infectious mononucleosis) were tested for the hepatitis A virus (HAV) and IgA anti-HAV by micro-solid-phase-radioimmunoassay. Only patients with hepatitis A were positive for HAV and/or IgA anti-HAV. In the first days of the disease we found HAV in the feces of 4 patients but it was never present after the sixth day. In all hepatitis A we found IgA anti-HAV in at least one fecal specimen and the titer of the antibodies increased in most cases during the course of the disease. The duration and the peak of the IgA response in the feces were strongly similar to other enterovirus infections. Some methodologic improvement both for HAV and IgA anti-HAV detection are suggested.