The efficacy of the collagen gel droplet-embedded culture drug sensitivity test (CD-DST) was estimated clinically among breast cancer patients to select a rational chemotherapy. Twenty-five specimens of breast cancer (n=21) or lymph nodes (n=4) were investigated. Four anticancer drugs (5-Fluorouracil, Adriamycin (ADM), Docetaxel (DOC), Paclitaxel (PTX)) were estimated for CD-DST. Sixteen samples among 25 samples (64.0%) seemed to be worth estimation. The chemosensitivity values were as follows: 5-FU 30.8%, ADM 30.8%, DOC 53.8% and PTX 46.2%, respectively. Thus, CD-DST may predict the chemosensitivity with high accuracy in breast cancer patients and seems to be superior to the conventional predictors.