Chronic morphine has been shown to decrease levels of neurofilaments (NFs) in the ventral tegmental area (VTA), which plays a critical role in the rewarding properties of morphine and other drugs of abuse. Since decreased levels of NFs are closely associated with a decrease in slow axonal transport, we studied the effect of chronic morphine on axonal transport in the VTA-nucleus accumbens (NAc) pathway. Chronic morphine decreased axonal transport from the VTA to the NAc by 50%. Chronic morphine did not alter axonal transport from the locus coeruleus to several of its projection areas, consistent with the lack of effect of chronic morphine on NFs in this brain region.