Improved procedures are described for the seeding of primary cultures from human colon adenocarcinoma and for the use of these cultures in the evaluation of drug effects. Two of the specimens studied were xenografts maintained in athymic (nude) mice, while the other six were biopsies obtained directly from patients. Tumor cells obtained directly from the patients proliferated in defined hormone-supplemented medium to the exclusion of other cells. In drug-response studies with cultures from a colon tumor biopsy all four drugs studied (4'-deoxydoxorubicin, 4'-O-methyldoxorubicin, 5-fluorouracil, and 1,3-bis-[chloroethyl]-1-nitrosourea) inhibited growth of the cells within 3-6 days after drug treatment. On an equitoxic dose basis (LD10 in mice), 4'-deoxydoxorubicin appeared to be the most active drug. This drug also showed dose-dependent activity against one of the xenografted tumors in vitro. In dose-response studies with cultures from another patient's colon tumor, doxorubicin and 5-fluorouracil showed significant activity against the tumor 10 days after the drug treatment with concentrations at 1X and 10X average peak plasma levels.