Monoclonal hybridomas secrete immunoglobulins with a single antigen sp
ecificity and distinct class/subclass structure. Hybridoma management
has commonly incorporated tests of antigen specificity into early scre
ening procedures, but has not typically utilized assays of immunoglobu
lin structure. In this article, we describe a technique of class/subcl
ass typing using polyvinylidene difluoride affinity membranes and a co
lorigenic enzymatic amplification system. The typing of monoclonal ant
ibody structure was sufficiently sensitive to permit its routine use w
ithin several weeks of hybridoma fusion. The information obtained from
early and routine class/subclass determinations included a semiquanti
tative assessment of monoclonal antibody concentration. In addition, t
he detection of a single immunoglobulin class/subclass in a microtiter
well supernatant supported the possibility that the colony was monoty
pic. The application of class/subclass typing and Poisson statistics t
o hybridoma fusions provided a numerical estimate of the probability o
f colony monotypia.