A free solution capillary electrophoresis method was developed to separate and quantitate codeine (CD), caffeine (CF), butalbital (BB), and aspirin (AP) in a mixture. The mixture was injected hydrodynamically for 5s at the anodic end and separation was performed on a fused silica capillary (72 cm × 50 μm i.d; 50cm to detector) at an applied voltage of 20 kV with 0.05 M phosphate run buffer pH 8. Separation was performed at ambient temperature and the total run time for analysis was 14 min. Detection was set at 220 nm. Calibration curves were prepared for CD, CF, BB, and AP with methyl p-hydroxy benzoate as internal standard. For each analyte, the correlation coefficients was greater than 0.999 (n=4). The RSDs % of ten replicate injections for each analyte were less than 1.4 %. The method was applied to the quantitation of CF, BB, and AP in a commercial tablet. Recoveries of the drug components were in the 96–104 % range.