AbstractA new combination of time, temperature, and alkali is described for the spectrophotometric determination of amoxicillin and ampicillin using Folin‐Ciocalteu reagent. The method is based on the development of blue‐coloured product due to the reduction of tungstate and/or molybdate in Folin‐Ciocalteu reagent by amoxicillin and ampicillin in alkaline medium. The chromogenic reaction has λmax at 720 and 740 nm with molar absorptivity 1.6295 × 104 and 0.1085 × 104 l mol−1 cm−1 in the Beer's Law range 2–10 µg mL−1 and 10–70 µg mL−1 for amoxicillin and ampicillin, respectively. The method is reproducible, quick, inexpensive, and particularly helpful in determining the drug content in commercial dosage forms. Copyright © 2010 John Wiley & Sons, Ltd.