CH40 and CH1500AA are newly prepared carbon suspensions which were examined as vital staining dyes for their usefulness in visualizing lymphatics at operation and to blacken lymph nodes. In mice, these carbon suspensions at 0.001 ml/g of body weight and India ink were injected subcutaneously into the footpad of the right hindpaw. Regional lymph nodes were visualized and were examined stereomicroscopically to determine how intensely these nodes blackened with carbon suspensions. Compared with India ink, CH40 and CH1500AA blackened the regional lymph nodes much faster and more vividly (1-8 min. after subcutaneous injection). As analyzed by centrifugal particle size distribution, CH40 and CH1500AA are narrowly distributed with a small particle size (150 and 167 nm, respectively, in mean diameter). By contrast, India ink is comprised of widely distributed and relatively large particles in suspension (mean diameter--254 nm). In 10 patients undergoing radical gastrectomy for treatment of stomach cancer, CH40 blackened 69% of regional lymph nodes with metastases (38 of 55) and 76% of those nodes without metastases (387 of 512).