A 3-generation study with two mating phases per generation and a teratology phase was performed in the rat to assess the reproductive and developmental toxicity of beta-cyclodextrin (beta-CD) in the diet. Transient neonatal growth retardation occurred with 5% beta-CD: a similar, but equivocal, effect was also observed with 2.5%. No permanent defects or other indications of developmental toxicity were found. There was no significant maternal toxicity. The dietary level of 1.25% was found to be a NOAEL for developmental toxicity. Further investigations showed the growth retardation to be specific to dietary administration during lactation: it was not produced by parenteral (i.p.) administration and was not influenced by treatment of the dams or litters during gestation. Slight maternal nutritional deficiency, caused by physico-chemical interactions of beta-CD with nutrients in the gut is proposed as the mechanism of action. No difference in milk composition was found.