Tests for biotyping isolates give a result that is classified as either positive or negative, indicative of growth or nongrowth of bacteria. The reproducibility of such tests is measured by the number of discordances in replicates of the same measurement. In this analysis the probability distribution of the number of discordances is estimated for each of several tests in the presence of possible random between-laboratory effects as well as random laboratory-test interactions, which are also estimated.