Strong flurothyl treatment (1.7% v/v for 8 min) produces retrograde amnesia in chicks when administered as long as 24 hr after one-trial avoidance training with a strongly aversive stimulus. Mild flurothyl treatment (0.2% v/v for 8 min) produced retrograde enhancement when administered as long as 16 min after similar training with a moderately aversive stimulus. The moderate training followed by mild flurothyl treatment enhanced 24-hr retention to the level found after strong training alone. Enhanced retention persisted for at least 72 hr; nonspecific performance effects faded within 48 hr. The predominant dose-dependent and time-dependent enhancement effect of mild flurothyl treatment is interpreted as improved memory consolidation.