This paper reports an LC/MS/MS method for analysis of salemeterol and fluticasone propionate in human plasma based on combined SPE-based extraction and separate LC/MS/MS conditions. Previously reported interaction between analytes was confirmed and eliminated by their separation in the sample preparation step to ensure no negative impact on their quantitation. The method was validated per FDA guidelines in the range of 2.5-500 pg/mL for salmeterol and 5-500 pg/mL for fluticasone propionate. The method is suitable for plasma analysis of combined salmeterol/fluticasone formulation without adverse effects of inter-analyte interactions on quantitation.