How long should toxicity tests in rodents last?

Lumley CE & Walker SR A critical appraisal of the duration of chronic animal toxicity studies Regulatory Toxicology and Pharmacology 1986; 6: 67-72.

Walker SR & Dayan AD A retrospective analysis of chronic toxicity case studies on pharmaceutical compounds. In Long-term Animal Studies: Their Predictive Value for Man. C.M.R. Workshop Series. Lancaster : MTP Press, pp. 53-62, 1986.