Crystallization is a thermal-seperation process widely applied in industry, especially in the chemical and pharmaceutical industries. The process is conducted with the purpose of obtaining a new solid phase. The properties of the product in the cystallization process considerably depend on the conditions under which the process is conducted. The desired distribution of both the size and form of the crystals can be achieved by adjusting the metastable zone width which reduces spontaneous nucleation and controls the crystallization process. Since it was not possible to determine the boundaries of the metastable zone in the experimental phase due to the specificity of the crystallization system, a theoretical review of the work is depicted, which adresses the influence of process parameters on the metastable zone width in crystallization of p-aminobenzoic acid in ethanol. In the experimental part the effects of solvents on the solubility of the active pharmaceutical ingredient of a pharmaceutical drug used for treating advanced lung cancer is analysed. The solubility of the active pharmaceutical ingredient was analysed in: water, methanol, ethanol, isopropanol, acetone, as well as in solvent mixtures: ethanol-water, isopropanol-water and acetone-water. The experimental results and obtained solubility curves indicate that ethanol, isopropanol and acetone are anti-solvents. The active pharmaceutical ingredient is precipitated from saturated solutions by adjusting the pH value by adding 10 % sodium hydroxide solution. Ethanol-water and acetone-water mixtures in volume ratio 3:1 were selected for further experiments and the dependence of the solubility of the active pharmaceutical ingredient on temperature is determined. Crystalscan was used to conduct crystallization by cooling and the efficiency of the system is determined.