This study is concerned with the histopathological changes and tumors and their incidences in the Wistar SPF Tox rat. Also included are data on survival, growth and haematology. The animals were untreated and were investigated for 30 months. The data are compared with those from two Wistar substocks, which had been used in the same laboratory: the Wistar CPB and the Wistar Conv. The results are summarized in tables and figures and are compared with data from the literature. A survey of studies dealing with spontaneous lesions and tumors in rats is given. A wide variety of tumor types and a relatively high tumor incidence were found in the Wistar SPF Tox rats. Since most of the tumors were found after 24 months, this high incidence was correlated with the life expectancy.