In vivo absorption characteristics of co-trimoxazole (Sulfamethoxazole- trimethoprim) from our commercially available oral suspensions have been studied. The absorption rate constant ranges for trimethoprim were 21.3 ± 2.8 x 10-2 hr to 32.2 ± 3.0 x10^-2 hr while for sulfatmethoxazole the ranges were 25.8 ± 2.7 x 10-2 hr to 32.1 ± 2.2 x 10^-2 hr variations between products were observed. However, it is possible that these variations reflect either intersubject variations in product performances. Keywords :