Background: Nitric oxide (NO) may alter dopamine release in the brain. Activation of D2-dopamine receptors may suppress NO synthase, and inhibition of NO synthase prevents behaviors induced by psychostimulants. We have investigated the modulatory actions of the precursor of NO synthesis (L-arginine) and the broad-spectrum NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on apomorphine-induced behaviors in the rat. Methods: Apomorphine was injected subcutaneously, and behaviors induced by the drug were examined in the presence or absence of intracerebroventricular administration of L-arginine and L-NAME. Results: Our data indicate that L-arginine or L-NAME treatment decreased licking and yawning, but not penile erection induced by apomorphine. Conclusion: Apomorphine-induced behaviors may be modulated by NO levels.