Data obtained from three systems are presented and discussed in reference to the problem of radioactive carry-over in boiling reactors. Measurements of droplet carry-over have been made on a small scale laboratory boiling test unit and on a 600-psia loop under high purity water conditions using Cs137 tracer. Measurements have also been made on the Borax-III boiling reactor under actual operating conditions. Activation products present in the steam and condensate served as an indication of the radioactive carry-over. Analysis of the decay curves of the samples provided a means of differentiating activities carried as droplets from volatile radioactive carry-over.