This paper presents data concerning the dose-effect relationships of intravenously administered amphetamine and cocaine on two widely used measures of psychomotor activation: locomotor crossover activity in neurologically intact rats, and rotational behavior in rats with a unilateral 6-hydroxydopamine lesion. There were marked differences in dose-effect relationships, both as a function of drug and of behavioral measure. Amphetamine produced a linear increase in rotational behavior over a wide range of doses (the highest effective dose was 76.8 times the lowest), but a linear increase in locomotor crossover activity over only a narrow dose range (the highest effective dose was only four times the lowest). In contrast, for cocaine, the dose-effect relationships for the two behaviors were very similar, but for both behaviors the effective dose range was quite narrow, the highest effective dose being only between two and four times the lowest. The data highlight the advantages and disadvantages of these measures as indices of the psychomotor activating effects of psychostimulant drugs.