Abstract These studies have examined the effects of the selective neurokinini 1 (NK 1) receptor antagonist CP-99,994 on the retching and vomiting response to apomorphine. CP-99,994 (1–3 mg/kg i.p.) attenuated retching and vomiting induced by apomorphine (0.25 mg/kg s.c.) with complete inhibition of retching and vomiting at the 3 mg/kg dose. In contrast CP-100,263 (3 mg/kg i.p.), the enantiomer of CP-99,994 with 1000-fold lower affinity for the NK 1 receptor, was without effect.