While powerful statistical methods have been available to taxonomists for almost half a century the extremely arduous and time consuming computations involved set a severe limit on their use. The development of electronic computers has facilitated a wider use of these methods, and the concept of basing quantitative assessments of affinity on qualitative as well as on quantitative attributes has led to the use of these methods in the investigation of classificatory problems within relatively heterogeneous groups. The results of a quantitative study of phenetic affinity amongst certain Phthiracaroiclea (Cryptostigmata) call into question the validity of some generic concepts, substantiate others and clravv attention to morphological criteria which might be used in the classification of the large and unwieldy genus Phthiracants Perty.