Histological and immunofluorescent assessment of the kidney, renal core cultures, and determination of circulating antibodies were carried out in Hartley guinea pigs with a selective delayed-type hypersensitivity state (DTH) and acute interstitial nephritis induced and elicited by exoantigens. The results show that the normal tubule-vascular structure of the kidney, the simplicity of the molecular structure of the exoantigens and the modification of the native form of the exoantigens, when it is presented to the kidney in the elicitation phase of the DTH reaction, are factors which may reduce the cellular response in the normal renal parenchyma. The cytological events over a 48-hour period are not different to those which have been described in DTH reactions in extrarenal tissues. Exoantigens can induce renal lesions evoking an acute interstitial nephritis picture in animals with selective DTH at a time when there are neither circulating antibodies nor deposition of immunoglobulins or infection in the renal parenchyma.