Immunoelectroosmophoresis was adapted as a rapid and sensitive microtechnic for differential detection of serum antibodies to several fungal and farmer's lung antigens. Multiple sets of wells were cut into agarose gels prepared on large glass microscope slides. Patients' sera in anodic wells with test antigens in opposing cathodic wells were electrophoresed for 90 min. Slides were examined for precipitin lines, then stained and dried for permanent reference. This technic proved more sensitive than conventional immunodiffusion for several of the representative specimens examined, but in no instance was it less sensitive. Because of this sensitivity, the reduction in time required, the small quantities of reagents used, the large number of samples accommodated, and its overall simplicity, immunoelectroosmophoresis should be applicable to routine mycoserology.