Abstract Five chemically modified starches, acetylated distarch phosphate, acetylated diamylopectin phosphate, starch acetate, hydroxypropyl distarch glycerol and phosphated distarch phosphate, were fed to rats at dietary levels of 0 (control), 5, 10 and 30% for 2 yr and at one level, 10%, over three generations. In the 2-yr study, no adverse effects were observed on mortality, food intake, haematology, blood biochemistry or urine composition. Each of the modified starches examined, except the phosphated distarch phosphate, slightly reduced body weights at the 30% level and caused distinct caecal enlargement at 10 and 30%, but the microscopic structure of the caecal wall was normal. In comparison with the controls, the males fed the 30% level of any of the modified starches showed a slightly increased degree and incidence of focal hyperplasia of the renal papillary and pelvic epithelium, accompanied by calcified patches in the underlying tissue. The studies did not provide any indication of carcinogenicity. The multigeneration study showed no effect on fertility, on lactation performance or on embryonic or pre-weaning mortality. Extensive microscopic examination of the F 3b-generation rats failed to reveal any changes attributable to treatment. It was concluded that the feeding of each of the modified starches at dietary levels up to 30% for 2 yr and at a level of 10% over three generations did not result in any distinct effect of toxicological significance.