The in vivo stability of standardized short ragweed concentrate (3.5 Amb a l u/ml) and dilutions were determined by means of parallel-line skin test. The freezer-line concentrates were reconstituted 50% glycerol and diluted using FDA approved HSA diluent. The mean dilution tested for stability was 0.0016 Amb a l u/ml (range 0.03 to 0.00016 or 1:2 hundred thousand, 1:7 thousand to 1:2 million). These dilutions were equipotent to the reference for up to 7 weeks. The concentrate was also stable at 7 weeks.
