Aflatoxin B1 administered intraperitoneally (i.p.) as a single dose to rats at a dose level of 3 mg/kg (the ld50) caused marked, but reversible, disaggregation of liver polysomes. Although disaggregation was not evident within 0.5 hr, it was extensive at 3 hr and persisted through 36 hr after dosing. Partial reaggregation began at 36 hr, and the process was essentially complete by 5 days after dosing. © 1969.