The solubility of pyridine-4-carbohydrazide (isoniazid) in ethanol, methanol, ethyl acetate, and acetone has been measured gravimetrically at various temperatures ranging from (301 to 313) K at atmospheric pressure. Isoniazid is most soluble in methanol, followed by acetone, ethanol, and ethyl acetate at a temperature up to 308 K. At higher than 308 K, isoniazid is most soluble in acetone. The experimental data were correlated using the modified Apelblat equation.