Mycotoxic nephropathy was induced in twelve 14 kg pigs fed a dietary component, moulded by Aspergillus ochraceus and contributing ochratoxin A at 1 or 3 ppm for up to 3 weeks. Concurrently, salmonellosis arose spontaneously in all six animals treated at 3 ppm and all died between days 15 and 17. Two of the six pigs in the 1 ppm group died similarly but the rest, and all of six control animals, were unaffected. Clinical biochemistry and histology revealed changes typical of renal ochratoxicosis in all ochratoxin-treated pigs. Clinical and pathomorphological changes typical of salmonellosis were evident in all those that died and Salmonella choleraesuis was consistently isolated from their faeces and liver. In a further experiment at 1 ppm ochratoxin A in animals immunised against S. choleraesuis haemorrhagic diarrhoea resulted instead, associated with Serpulina hyodysenteriae and Campylobacter coli. There was concomitant evidence of immunosuppression and delayed response to immunization. For the first time, susceptibility to natural infectious disease has been demonstrated in pigs exposed to the immunotoxicity of ochratoxin A. Differentiation of biochemical and histological changes attributable to ochratoxicosis or to secondary disease may require reinterpretation of a classical description of experimental porcine ochratoxicosis.