The genus Streptomyces is the most important and intensively studied m
ember of the actinomycetes. Definition of its species has been and rem
ains difficult for a variety of reasons. The application of numerical
techniques to the problem is reviewed over the period 1960-1990. The e
fficiency and relevance of numerical techniques based on phenetic char
acteristics are assessed by consideration of rapid, miniaturized tests
, the impacts of genetic manipulations on probabilistic identification
s and correlations of numerical phenetic data with those provided by c
hemical and molecular techniques.