Several experiments were performed with rats in order to investigate the stimulus conditions affecting the rate of acquisition of two‐way active avoidance. The number of trials per session, the duration of the Conditioned Stimulus (CS), the intertrial interval (pause time), and the intensity of the shock presentation were each varied in separate experiments. The optimal, yet practicable, conditions required to obtain a fast rate of acquisition included 40 to 60 trials per session, a 40‐sec intertrial interval, a 10‐sec Conditioned Stimulus presentation and a shock intensity of 1.0 mA. These results are discussed with regard to the problem of standardization in behavioral research manipulating biological independent vari