The relative toxicity of 14 normal aliphatic alcohols has been determined as 48-hr 50% population growth inhibition (log BR, biological response) of Tetrahymena pyriformis. A linear relationship was observed between log BR and the 1-octanol/water partition coefficient (log Kow). Comparison of log BR with 96-hr 50% mortality data for Pimephales promelas revealed excellent agreement between the two test systems. A relatively constant steady-state biophase toxicant concentration is calculated for each alcohol. Calculated chemical activity increased with an increase in hydrocarbon chain length. In addition, there was good agreement between chemical activity and the activity coefficient for narcosis.