Delayed-type hypersensitivity response induced by peptides in guinea-pigs. Guinea-pigs were sensitized with 200 μg M. leprae in Freund’s incomplete adjuvant and - after 30 days - were inoculated intradermally with peptides and controls. Each group contained five animals. The result in 48 hours after application of 10 μg peptides, Mistsuda lepromin (M) with 4 × 106 bacilli and 10 μg soluble extract of M. leprae (ML) is indicated. The peptide pool contain equimolar amounts of the three peptides. The diameter of the reaction corresponds to the average of horizontal and vertical diameters of the erythema. 0.9% NaCl (C) was used as negative control. * The animal responded after 72 hours. ** The animal responded after 21 days.