Frequency and size distribution of micronuclei in lymphocytes stimulated with phytohemagglutinin and pokeweed mitogen in workers exposed to piperazine

30 male workers exposed to piperazine and the same number of controls were investigated. Parallel lymphocyte cultures with pokeweed mitogen and phytohemagglutinin were set up and the cells were analyzed regarding frequency and size of micronuclei. There was a statistically significant effect of the occupational exposure on the micronucleus frequencies and sizes as well, but only in the cultures activated with pokeweed mitogen. The two mitogens may activate different lymphocyte subpopulations, which probably explains both the present and earlier in vitro findings. It is interesting that there is an increased frequency of B cell derived tumours (non-Hodgkin's lymphomas and myelomas) in the piperazine-producing plant.