The purpose of this study was to investigate the fate and effects of mineral oil saturated hydrocarbons (MOSH) in female Fischer 344 rats. Animals were fed control diet or diet containing various MOSH mixtures at concentrations ranging from 40 to 4000 mg/kg feed for up to 120 days. MOSH were analysed in liver, spleen, adipose tissue and remaining carcass at different sampling times. In addition to clinical effects, liver microgranulomas, hepatic inflammation, and disruption of the immune function were the main toxicological endpoints investigated. Arthritis symptoms were specifically studied in dark agouti rats. The results indicate that accumulation of MOSH depends on the mixture tested but always occurred predominantly in the liver and to a lesser extent in adipose tissue and spleen. Strong differences exist between liver and adipose tissue in terms of accumulated hydrocarbons: whereas in adipose tissue the accumulated fraction corresponds to the most volatile part of the administered mixture, in the liver, the most volatile as well as the highest boiling part of the mixture are almost absent. Also the types of hydrocarbons differ. When exposure ceases, a significant decrease of MOSH concentration was observed in the liver, but not in adipose tissue. MOSH exposure results in a significant increase in absolute and relative liver weights, the effect being dose-related, but also dependent on the mixture tested. There were large differences in the ability of the different mixtures to induce liver granulomas. The highest incidence was observed with the mixture containing the highest proportion of n-alkanes, suggesting that this fraction could play a significant role in the development of hepatic granulomas. No effects were found on the immune function, irrespective of the mixture or the dose tested.