Comparison of lymphocyte transformation responses to fresh or frozen phytohemagglutinin

Peripheral blood lymphocytes were cultured in microtiter plates with phytohemagglutinin which was added on the day of testing or had been previously pipetted and frozen. There was good correlation of transformation results using PHA concentrations from 0.25 to 10 microgram/ml (r = 0.772) to 0.828) PHA could be prepipetted and frozen for up to four weeks maintaining good correlation.