Fluorescence intensity correlation functions of single terrylene molecules in p-terphenyl crystals were measured within the temperature range 5-300 K. The analysis provided the population (k(23)) and depopulation (k(31)) intersystem crossing (ISC) rate constants of the lowest excited triplet state T-1. These rates increase continuously with temperature, without any noticeable change at the 193 K, temperature of the order-disorder phase transition in p-terphenyl crystal. The depopulation channel composed of the exciting light intensity dependent T, -> T-n, absorption followed by the T-n -> S-1 ISC is important at higher temperatures. (c) 2005 Elsevier B.V. All rights reserved.