Using a laser monitoring observation technique, the solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water have been determined experimentally from 292.65 to 361.35 K. The experimental data are correlated with the lambdah equation. The calculated results show good agreement with the experimental data. The fusion enthalpy of niacin was determined by using DSC. The excess enthalpy of solution HE is estimated for each system on the basis of the calculated parameter h and the measured enthalpy of fusion. (C) 2004 Published by Elsevier B.V.