Slight structural molecular variations are known to affect different properties of compounds. In solution, different solute-solvent interactions are known also to alter the properties of numerous compounds. Quantitative structure-activity relationships (QSAR) are used regularly to analyze and predict the variations of different properties of compounds that are caused by structural variations and significant solute-solvent interactions. The relative basicities of n-propylamine, dipropylamine and tripropylamine were determined in nine different solvents from potentiometric titrations. QSAR that were developed from these experimental basicity values were used to evaluate the type and significance of the solute-solvent interactions. The important interactions that influence basicity variations for the propylamines studied are dipolarity-polarizability interaction between the solute and the solvent and hydrogen bonds from the propylammonium ions to basic solvents. The role of hydrogen bonds from the propylamines to acidic solvents is minor.