In the first set of experiments, biologic activity of VA was determined by the enhancement of viral onco- genesis. In these experiments, freshly infected cells were treated with VA and after 3 weeks, the number of virally transformed foci were counted and the frequency of transformation dete'rmined by calculating the number of viral foci per 10s surviving cells. In each of two experiments, significant enhancements of viral transformation was observed at concentrations ranging from 62.5 to 1000 ug/L. Details of the method and data with other chemicals can be found in papers on the enclosed Reference list. This technique has been very effective in detecting carcinogens and mutagens of varies classes and a data-base of approximately 160 chemicals has been achieved in our laboratory. .