The beta-adrenergic antagonists sotalol, nadolol and timolol (which act at both beta 1- and beta 2-receptors) induce amnesia in the domestic chick when given systemically after a one trial passive avoidance task. State dependent learning and effects on performance at test (e.g. interference with recall) almost certainly do not cause the observed amnesia. All three effective beta-antagonists induce amnesia only when injected within a limited period after training, suggesting effects on memory formation. Sotalol differs markedly from nadolol and timolol in: (a) showing a sharp and markedly earlier loss of effectiveness as administration is moved to progressively later times after training (25-30 min rather than 40-50 min), (b) producing when given after training a delayed and gradual loss of retention rather an immediate and rapid loss. These differences seem not to reflect a lesser effectiveness of sotalol, nor a greater delay in the onset of its action, but instead qualitative differences in effects on memory formation.