Abstract The Center for Analytical Chemistry of the National Bureau of Standards is actively engaged in research to provide the basis for quality assurance in chemical measurements of rain water. Several types of SRMs are currently available which have direct applicability to atmospheric deposition programs. In addition, research is proceeding to develope and SRM specifically for rain-water analyses. Initial attempts, using a single solution containing all the components of rain and stored in glass ampoules, were unsuccessful due to the chemical instability of the solution. Current efforts are directed to improving the stability by using polyethylene bottles to store the solutions, and by preparing two separate solutions, one for the major components of rain (sulfate, nitrate, chloride, sodium, potassium, calcium, magnesium, ammonium, and hydrogen ions), and the other for the trace metals. Preliminary results on the stability of a pilot set of simulated rainwater solutions are encouraging.