This method provides information on health hazard likely to arise from exposure to test substance via oral administration. The determination of sub-chronic oral toxicity using repeated doses may be carried out after initial information on toxicity has been obtained from acute or repeated dose 28-day toxicity tests. The method is based on the repeated oral administration of the substance of interest over a prolonged period (one dose level daily during 90 days). This Test Guideline is intended primarily for use with rodents (rat preferably). At least 20 animals (10 female and 10 male) should be used for each test group. Three concentrations, at least, should be used. The test compound is administered by gavage or via the diet or drinking water. A limit test may be performed if no effects would be expected at a dose of 1000 mg/kg bw/d. The results of this study include: measurements (weighing at least once a week, food and water consumption) and daily and detailed observations (ophtalmological examination, haematology, clinical biochemistry and urinalysis), each day preferably at the same time; as well as gross necropsy and histopathology. A number of endocrine-related measurements, particularly relevant to thyoid function have been added in 2018. A properly conducted 90-day subchronic test should provide a satisfactory estimation of a no-effect level.