PURPOSE: For decades, systemic medical treatment for colorectal cancer has been limited almost entirely to 5- fluorouracil (5-FU). In cases of advanced colorectal cancer, the response rate to standard 5-FU regimen was lower than 20%. Recently, new drugs that have another action mechanism have been introduced-irinotecan, oxaliplatin, raltitrexed, capecitabine, etc. Clinicians have to choose the appropriate drug for advanced cases. Until recently, choice of chemotherapeutic agents was based on the experience of clinicians, or on retrospective or prospective clinical trial reports. In this study, we performed HDRA (histoculture drug response assay) to assess the effectiveness of chemotherapeutic agents in colorectal cancer. METHODS: Tumor specimens of 33 colorectal cancers were collected in 15 ml tubes containing PBS buffer. Tissues were minced using an autoclaved knife and histocultured on collagen sponge gel matrix, followed by treatment with 5-FU, 5-FU & leucovorin, oxaliplatin, oxaliplatin & 5-FU, irinotecan, or irinotecan & 5-FU. After 48 hours, cell viability was assessed by MTT assay. The inhibition rate of each drug was calculated for relative survival. Cases of drug responsibility below 30% were regarded as drug resistant cases. RESULTS: Thirty cases were tested. Three cases had synchronous lesion. Thirty-three tissues were evaluated using HDRA. Seventeen cases (53.3%) were rectal cancer. The initial 6 cases were tested using a single agent the other 27 cases were tested using combined agents. The regimen showing the best responses was oxaliplatin with 5-FU (8/26 cases, 30.8%). Seven cases were regarded as chemoresistant cases because they showed low IR below 30% for all agents. Synchronous lesions showed similar drug responses. CONCLUSION: HDRA is relatively simple and easily applicable to in vitro study to determine the appropriate chemotherapeutic agents. Further study is necessary to assess the effectiveness including tumor recurrence and survival.