Background.-As silver diamine fluoride (SDF) gains popularity for caries arrest, the authors aimed to investigate the content of fluoride and silver in 38% SDF produced for the US market and its short-term stability. Methods.-Five samples of 38% SDF were evaluated when the bottle was first opened, and at 7 and 28 days. Fluoride concentrations were determined with a fluoride ion-selective electrode, and silver concentrations were determined with a simultaneous inductively coupled plasma mass spectrometer. pH was measured with a pH probe. Weight and volume of individual drops were measured. Results.-At day 0, 40% of individual measured values were above the expected fluoride concentration, and at day 28, 93% were above the expected fluoride concentration (P = .005). At day 0, 19% of individual measured values were below the lowest expected silver concentration, and at day 28, 93% were below (P < .001). Acidity (pH 10) was consistent over the 3 periods. Mean (standard deviation) weight of a drop was 40 (4.0) milligrams, and mean (standard deviation) volume was 32.55 (1.89) microliters, 30% more than the reported value of 25 μL. Conclusion.-Over 28 days, the product pH is stable, whereas the fluoride content tends to increase and the silver content tends to decrease. Drops were larger than expected when dispensed from the bottle.