This is the first report of transparent exopolymer particle (TEP) concentrations within deep-sea hydrothermal vent systems using colorimetric methods, measuring TEP in supernatants of sediments surrounding the vents, in fluids emanating directly from hydrothermal vents and in neutrally buoyant hydrothermal plumes. Samples were collected at Guaymas Basin (Gulf of California), a sedimented hydrothermal system. TEP concentrations within the hydrothermal fluids were significantly greater than the only other report of TEP in deep water. The range of values for TEP abundance were 8–6,451 μg/L of gum xanthan equivalents, the highest values being associated with supernatants of microbial mat-covered sediments. The potential sources and significance of the high concentrations of TEP observed in this deep-sea hydrothermal environment are discussed.