The effect of additives on the temperature of precipitation of a nonionic surfactant from micellar solutions is studied experimentally and on the basis of thermodynamic relationships for the pseudophase separation model. The derived formulas connect the decrease in the precipitation temperature (Delta T effect) produced by amphiphilic additives with the composition of mixed micelles "basic surfactant-additive" and also with the temperature and the heat of the dissolution of the individual surfactant. Experimental data on the dissolution temperatures of crystalline N-dodecanoyl-N-methylglucamine (MEGA-12) in aqueous micellar solutions containing additives of various chemical nature are presented; the data for systems with alkanol C-2-C-4 additives relate to a wide range of the surfactant and alkanol concentrations. The enthalpies of dissolution of the crystalline MEGA-12 in water and water-alkanol mixtures determined by the Calvet calorimetry are given. The dependencies of the Delta T effect on the concentrations of MEGA-12 and alkanol (ethanol, propanol, or butanol) calculated from the model are in good agreement with the experimental data. The composition of mixed micelles formed by MEGA-12 and an alkanol C-2-C-4 is found from the Delta T data with the help of the model; the distribution of the alkanols between the micellar and aqueous pseudophases is evaluated. Nonideality of the aqueous alkanol solutions is taken into account in the model calculations. The results of measurements for aqueous and aqueous-alkanol mixtures of MEGA-12 containing salt additives evidence that the addition of salts (potassium, sodium, and ammonium chlorides, nitrates, carbonates, and sulfates) to aqueous solutions of MEGA-12 does not change significantly the temperature of the solid surfactant-micellar solution equilibrium, but a pronounced decrease of the temperature is observed when the salts are added to aqueous MEGA-12 mixtures containing alkanols, which is in correspondence with the model predictions.