Two types of SiO2 were used in a proportion of 0.100 g per 0.01 L nicotinamide solns. in acetonitrile (concns. 250-7150 mg/L) to det. nicotinamide adsorption isotherms at 25 degrees C by using the Freundlich, Jovanovic, Langmuir and Dubinin-Astakhov models. Non-linear matching anal. and the sum of normalized errors were used to est. isotherm parameters and det their optimal values, resp. Adsorption of nicotinamide on silicas was best described by the Jovanovic and Dubinin-Astakhov models