The effects of nicardipine treatment on collar-induced intimal thickening and on accompanying reactivity changes in rabbit carotid artery have been investigated. Treatment for three weeks with subcutaneous nicardipine (20 mgkg(-1) per day) significantly inhibited the intimal thickening caused by perivascular application of a silicone rubber collar. Potassium chloride (KCl), phenylephrine and 5-hydroxytryptamine (5-HT) induced concentration-dependent contractions in both sham-operated and collared arteries. Collar-induced attenuation of maximum KCl-, phenylephrine- and 5-HT-induced contraction was not affected by nicardipine. Collaring caused the means of pD2 values (the negative logarithm of EC50 values, 50% effective concentration) of 5-HT and phenylephrine to increase and decrease, respectively. Nicardipine did not affect the altered sensitivity to these agonists. Neither collar implantation nor nicardipine treatment altered the pD2 values for acetylcholine- and nitroglycerine-induced relaxations. These results demonstrate that nicardipine inhibits collar-induced intimal thickening in rabbit carotid artery without affecting the accompanying changes in vascular reactivity, indicating a possible lack of association between the development of intimal thickening and altered reactivity.