The collagen gel droplet-embedded culture drug sensitivity test (CD-DST) is one of the best chemosensitivity tests owing to its high success rate. However, CD-DST is often a culture method, and contamination is a serious problem, especially in the case of colorectal cancer, which is contaminated by enteric bacteria. It has been reported that the success rate of CD-DST is 64.0% in the case of colorectal cancer. Therefore, the sampling and washing of specimens before culture are extremely important. By washing specimens carefully with normal saline containing antibiotics, we achieved a success rate of 85.3% in the case of colorectal cancer. To improve the success rate, we started specimen irrigation with a large amount of normal saline in January 2007. As a result, a success rate exceeding 90% was acquired. For the success of CD-DST for colorectal cancer, it is important to irrigate specimens many times with a large amount of normal saline.