Twenty-five badgers, captured in an area where they had been implicated in outbreaks of bovine tuberculosis, received intradermal inoculations of control medium, 150 micrograms phytohaemagglutinin (PHA), 40 units streptokinase/10 units streptodornase (SK/SD), 200 micrograms purified protein derivative of Mycobacterium bovis (PPD), Freund's incomplete adjuvant (IFA), and Freund's complete adjuvant (CFA), each in 0.1 ml of inoculum. The reactions were assessed by skinfold thickness and skin histology 30 min--7 days after inoculation. Control medium caused slight cellular reaction, mostly polymorphonuclear leucocytes (PMNs), but no significant increase in skinfold thickness. SK/SD provoked no reaction. PHA stimulated a marked increase in skinfold thickness; the cellular reaction was predominantly PMNs, with some macrophages occurring after several days. IFA and CFA promoted a long-lasting increase in skinfold thickness, and a mixed histological picture of PMNs and macrophages; later in the response, especially to CFA, giant cells and some lymphocytes occurred. PPD stimulated a small increase in skinfold thickness with a timing (2-3 days) consistent with delayed hypersensitivity (DTH); there was, however, no erythema or palpable oedema or induration. The histology was an initial multifocal reaction of PMNs with a later phase of lymphocytes and macrophages with some granuloma formation. Other cell types (eosinophils, basophils) were seen in varying proportions in all reaction sites. M. bovis was isolated from four badgers; the cellular reaction to PPD was stronger than in uninfected animals, but other aspects of the skin response were unaffected. This study shows the capacity of badgers for strong inflammatory responses, and is the first report of a DTH response to PPD in this species.