Reagent 1: Mix one volume of reagent B (0.5% copper sulfate pentahydrate, 1% sodium or potassium tartrate) with 50 volumes of reagent A (2% sodium carbonate, 0.4% NaOH). Both reagents A and B are supposed to be stable for a long time but I have had a problem with precipitation in reagent B that seems to be remedied by adding a little NaOH.
Reagent 2: Dilute commercial Folin-Ciocalteu phenol reagent with an equal volume of water. Stable for a few days or weeks.
To quantify protein, mix 0.25 mL of protein with 2.5 mL of Lowry reagent 1. After 10 minutes, add 0.25 mL of Lowry reagent 2 and mix well immediately. After 30 minutes, measure the absorbance at 750 nm (if you're using a Spectronic 20 with a normal phototube, 750 is too long; 600 nm gives lower absorbances but works okay).