Meaningful applications of water geothermometry to thermal springs in and around Lassen Volcanic National Park (LVNP) are limited to Growler Hot Spring and Morgan Hot Springs. Most hot springs located within LVNP are low-chloride, acid-sulfate waters associated with nearby steam vents. This type of hot-spring activity is characteristically found above vapor-dominated hydrothermal systems. These acid-sulfate waters are not generally useful for liquid chemical geothermometry, however, because their chemical compositions result from water-rock interaction at relatively shallow depths. Thermal waters at Drakesbad and in Little Hot Springs Valley have neutral-pH, low-Cl concentrations and have estimated Na-K-Ca and Na-Li geothermometer temperatures close to measured spring temperatures of 65 to 95??C. Hot-spring waters located south of LVNP at Growler Hot Spring, Morgan Hot Springs, and in the south-central part of LVNP in the Walker "O" No. 1 well at Terminal Geyser are rich in chloride and yield calculated geothermometer temperatures between 220 and 230??C. These thermal waters probably originate within a zone of upflow of high-enthalpy fluid inside LVNP and cool conductively during lateral flow to the south and southeast. ?? 1985.