For many procedures used in behavioral pharmacology, the intracerebroventricular (ICV) route of drug administration is infrequently used due, in part, to the lack of a reliable technique for determining cannula patency in vivo. This study describes an in vivo technique for assessing ICV cannula patency in pigeons. The technique was applied in an experiment designed to evaluate several drugs, which are presumed to differ in the extent to which they enter the central nervous system, for their rate-suppressing effects in pigeons trained to peck a key on a fixed-ratio 20 schedule of food reinforcement. The opioid agonist morphine and antagonist quaternary naltrexone were 100 and 280 times more potent, respectively, in suppressing responding when administered ICV, as compared to systemic administration. Tertiary naltrexone was approximately equipotent as an antagonist of morphine's rate-suppressing effects when administered ICV or systemically. Quaternary naltrexone did not antagonize morphine by either route of administration. The utility of this in vivo cannula verification technique is discussed, as well as the limitations of comparisons between systemically-administered tertiary and quaternary derivatives.