Although the exact nature of the biological effects of microwaves is not completely understood, evidence indicates that organisms exposed to microwaves at specific frequencies and power densities can experience thermal stress. Power density, duration of exposure, environmental temperature, and drugs that affect temperature regulation influence the response. Reported effects of microwave exposure on the eye, hematopoiesis, thyroid function, gonads, and central nervous and cardiovascular systems are reviewed and analyzed to indicate relevance or lack of relevance to RF and microwave exposure; to decipher the known and substantiated effects from those that are purely speculative and to provide a realistic perspective on the possible effects of exposure to this form of energy. Enactment of PL 90-602 “Radiation Control for Health and Safety Act of 1968” has evoked renewed interest in safety “Standards” for microwave exposure. The standard recommended in 1953 and subsequently adopted has been maintained with slight modification to this date. The adequacy of the originally proposed standard, namely, 10 mW/ cm2 has been questioned from time to time, but as in the past, there is little reason to require modification of this Standard.