The stability of valacyclovir hydrochloride in three commonly used syrups was studied. Triplicate suspensions of valacyclovir (from caplets) in Ora-Sweet (Paddock Laboratories), Ora-Sweet SF (Paddock), and Syrpalta Humco Laboratory) syrups were extemporaneously compounded to yield a final concentration of valacyclovir 50 mg/mL (as the hydrochloride salt). The nine suspensions were stored at 4 degrees C in amber glass bottles. At intervals up to 60 days, the liquids were visually inspected for color change, cloudiness, gas formation, and precipitation, and samples were assayed in duplicate for valacyclovir concentration by stability-indicating high-performance liquid chromatography. Also tested were pH, particle size, and microbial growth. During the first 21 days of storage, mean valacyclovir concentrations in all liquids were >90% of the initial concentration, but concentrations were <90% by day 21 in some individual samples of suspensions prepared with Ora-Sweet and Ora-Sweet SF. Mean valacyclovir concentrations in the Syrpalta-based suspensions met the 90% cutoff for at least 35 days. Solution pH and particle size remained unchanged in all liquids through day 60, and there were no changes in physical appearance. There was no evidence of microbial growth on the days when microbial growth was tested (0 and 28). Valacyclovir 50 mg/mL (as the hydrochloride salt) in three oral liquids stored in amber glass bottles at 4 degrees C was stable for at least 21 days when prepared with two of three syrups and for at least 35 days when prepared with the third syrup. All the liquids were free of microbial growth for at least 28 days.