Tritiated latex particles and scintillant latex particles have been covalently coated with an antigen (human albumin) and both types of particles are than combined in dilute aqueous suspensions. The formation of antibody-induced dimer and higher-order aggregation resulted in scintillations that could be measured in a standard liquid-scintillation counter, energy-gated for H-3. Rabbit anti-human antiserum was easily detected at a titer of 1:10(6). Human albumin, in the inhibition mode, was also easily detected at 0.1 ng/ml. Since the samples are nondestructively assased, it was possible to examine the kinetics of aggregation under a variety of conditions.