Various central stimulant drugs were tested in mice subjected to five daily 100-trial avoidance sessions in the shuttle-box. Facilitation of avoidance responding was observed following i.p. administration of metamphetamine and cocaine, but not following methlyphenidate, caffeine, pentetrazole and strychnine. Some favourable effects were obtained by combining the above stimulant drugs with cholrdiazepoxide. Advantages in the combination with chlordiazepoxide were particularly evident in the case of methamphetamine.