We performed a crossover study of apomorphine-induced motor response reproducibility in 10 parkinsonian patients with the "on-off" phenomenon. On 2 separate days, each patient received two successive identical s.c. apomorphine injections, the second injection being randomly administered either 10 or 80 min after the end of the first apomorphine-induced motor benefit. Latency (12.3 +/- 4.5 min) and duration (61.9 +/- 13.3 min) of motor effects were similar in all tests. A transient worsening of the parkinsonian state after a motor improvement induced by apomorphine occurred in most of the patients. Therefore, the duration and severity of the "off" period after a motor improvement does not seem to influence the efficacy of a second apomorphine administration.