The therapeutical action of diuretics has been attributed to their hydrophobic character, among other properties. Therapeutical and physiological classifications of diuretics are correlated. The site of action of high efficacay diuretics is the loop of Henle, that of intermediate efficacy diuretics is the distal tubule and that of low efficacy diuretics is the proximal and distal tubules, and the collecting duct. Partition coefficients between water and micelles offer a scale for hydrophobicity, which leads to a further correlation between retention in Micellar Liquid Chromatography (MLC), with a sodium dodecyl sulphate mobile phase and an ODS-C18column, and the sites of action within the nephron. The site of action of those diuretics showing the lower retention in MLC is the proximal tubule (acetazolamide) and the loop of Henle (loop diuretics), for those diuretics with an intermediate retention is the distal tubule (thiazides), and for those with a long retention is the collecting duct (potassium sparing diuretics).