After guinea pigs are sensitized with protein antigens in saline or incomplete Freund's adjuvant (IFA), delayed-onset skin reactions elicited at early intervals have certain distinctive immunogenic requirements and unique histologic features that set them apart from classic delayed hypersensitivity. These reactions have been called “Jones-Mote” or cutaneous basophil hypersensitivity (CBH). In the present study lesions induced with insoluble antigen-antibody complexes in IFA have similar histologic characteristics and could also be regarded as examples of CBH. Delayed reactions elicited in animals sensitized with protein antigens in complete Freund's adjuvant (CFA) included numerous basophils when tested early after sensitization; however, at later intervals, this component became less prominent. Delayed lesions of contact allergy to dinitrofluorobenzene/dinitrochlorobenzene (DNFB/DNCB) similarly contained a prominent basophil component that was not diminished when testing was delayed for several weeks following sensitization. Immunization with DNFB in CFA sensitized animals for contact reactions that were more intense and indurated and contained a somewhat smaller proportion of basophils. CBH was passively transferred with lymph node cells from sensitized animals (but not with serum). Reactions in recipients were weak but histologically characteristic. Neither compound 48/80 nor specific antigen caused basophils to degranulate. Basophils did not accumulate one antigen tested, iodinated human serum albumin.