The human glioma-derived cell line D-54 MG and the human medulloblastoma-derived cell line TE-671 have been shown to be sensitive in culture to the pharmacological interference with glutamine metabolism by acivicin, 6-diazo-5-oxo-L-norleucine, and methionine sulfoximine. Using as a guide the multiple contributions of glutamine to the biosynthesis of proteins, purines, and pyrimidines, we now have identified six additional antimetabolites active against these lines in vitro at clinically relevant concentrations. The 50% growth-inhibitory levels of the drugs against D-54 MG in 6-day continuous exposure experiments were: L-asparaginase, 0.057 IU/ml; 5-fluorouracil, 0.5 micrograms/ml; 6-mercaptopurine, 0.8 micrograms/ml; actinomycin D, 0.0007 micrograms/ml; N-phosphonacetyl-L-aspartic acid, 2.3 micrograms/ml; and 5-azacytidine, 0.2 micrograms/ml (3-day exposure. The corresponding 50% growth-inhibitory values in TE-671 were: L-asparaginase, 0.54 IU/ml; 5-fluorouracil, 1.5 micrograms/ml; 6-mercaptopurine, 4.7 micrograms/ml; actinomycin D, 0.00044 micrograms/ml; N-phosphonacetyl-L-aspartic acid, 4.5 micrograms/ml; and 5-azacytidine, 0.49 micrograms/ml. Dipyridamole up to 10 micrograms/ml was inactive against both lines. The isobologram method was used to evaluate the effectiveness of several two-drug combinations which were biochemically designed. The sums of the optimal fractional inhibitory concentrations for the pairs were: acivicin plus L-asparaginase, 0.14; acivicin plus methionine sulfoximine, 0.40; 6-diazo-5-oxo-L-norleucine plus methionine sulfoximine, 0.60; acivicin plus 6-mercaptopurine, 1.0, all in TE-671; and acivicin plus 5-fluorouracil, 0.79, in D-54 MG. Our findings suggest that an antimetabolite regimen exploiting glutamine sensitivity might improve the chemotherapy of some human gliomas and medulloblastomas.