The cytotoxic agent acivicin has been shown to be effective against several types of tumors. However, the clinical utilization of acivicin has been prohibited because of its dose-limiting neurotoxicity. Acivicin is believed to be transported into the brain by the large neutral amino acid (LNAA) carrier, which is expressed at the blood-brain barrier (BBB). In this study, we used an in situ rat brain perfusion technique to determine the kinetics of the LNAA carrier-mediated transport of acivicin across the BBB. We found that the Vmax of acivicin (1.05 nmol/sec/g) obtained in this study was comparable to the Vmax of L-leucine (1.07 nmol/sec/g) and other LNAAs as determined by other investigators. The Km was high compared with other LNAAs, but this could be explained by the low lipophilicity of acivicin. Acivicin transport across the BBB was inhibited by other LNAAs but not by acivicin derivatives with structural modifications at the amino or carboxyl group. The ASC (alanine, serine, cysteine) carrier system did not influence the transport of acivicin across the BBB. These results suggest that the CNS toxicity of acivicin might be reduced by coadministration of other LNAAs. Acivicin derivatives with structural modifications at the amino or carboxyl group of acivicin lack affinity for the LNAA carrier at the BBB and, therefore, will exhibit less CNS toxicity than acivicin.