Measurements of the cloud point (CP) of non-ionic surfactant polyoxyethylene (20) sorbitan monooleate (Tween 80) were performed in aqueous solution and in the presence of ceftriaxone sodium trihydrate (CFT) drug, with specific attention to CFT drug + different salts mixtures studied and discussed in detail. The CP values of Tween 80 in aqueous medium tend to reduce with enhanced concentration of surfactant. The CP values of Tween 80 solutions were also found to be decreased with increasing concentrations of drug used. The CP values of Tween 80 + drug mixtures were found to be lower in magnitude in the presence of salts in comparison to their absence, and the outcomes of sodium salts (between 0.001 and 0.2 mol.kg(-1)) in reducing CP values were found to be in the following order: NaCl < Na2SO4 < Na2CO3. In the case of potassium salt the order of reducing the CP values of Tween 80 + drug is similar, but in the case of ammonium salt the order is NH4Cl < Na2CO3 < (NH4)(2)SO4. The influence of cationic co-ions such as Na+, K+, and NH4+ on decreasing the CP of Tween 80 + drug solutions is found to be in the following order: NH4Cl < KCl < NaCl, (NH4)(2)SO4 < K2SO4 < Na2SO4, and (NH4)(2)CO3 < K2CO3 < Na2CO3. The values of Delta G(c)(0) were achieved to be positive for the total studied solutions which indicates the nonspontaneous nature of clouding. The Delta H-c(0) and Delta S-c(0) values were found to be negative in almost all cases in the presence of salts except for the CFT + water system. The negative values of Delta H-c(0) and Delta S-c(0) decreased with increasing concentrations of salts.