A sensitive method of evaluating the dose absorbed during exposures to 2450 microwaves has been established by measuring light emission from a suspension of luminescent bacteria stabilized in a non-dividing form. Mutation frequencies are measured in these bacteria subsequent to exposure by the method of auxotroph reversion. This exposure system will be used to study forward mutation among the genes controlling light emission by identifying the frequency of colonies on plates which emit light at 23 C but not at 37 C. Since cell division and mutation are related, we will also develop an exposure procedure in which light emission can be followed in growing cells during microwave exposures. This will enable us to evaluate mutation in dividing cells and also to chronically expose cells to lower dose rates over longer time periods. To make the data more representative of diverse species, other microorganisms whose genetics has been more extensively studied will be exposed under conditions identical to those used with the luminescent organisms and the mutation frequencies will be evaluated. We are currently attempting to obtain a continuous wave source for attachment to our exposure chamber. If one is obtained, we will compare mutation frequencies produced by continuous as well as pulsed sources. The same techniques of measuring absorbed dose will be utilized for both.