The data also suggest that mutagenic effectiveness is not necessarily directly related to the number of aziridinyl groups since compound\ such as 5 and 7 were nearly as effective as 2, and 8 was more active. When the nonheteroaromatic compound5 9, 10, and 11 were tested for recovery, the number of recovered dominant lethal mutations did not decrease after stor-: i:; e for 7 days.