A multidisciplinary approach was employed to assess the possible biological effects of chronic exposure of rats to 100-MHz continuous wave (CW) radiofrequency (RF) radiation. A group of 20 time-bred rats were exposed in a transverse electronmagnetic mode (TEM) transmission line to 100-MNz at a forward power of 500 W (46 mW/sq. cm.) starting on Day 6 of gestation under controlled temperature and humidity conditions. Pregnant dams and later their offspring were exposed daily for 4 hr for up to 97 days of age. An equal number of sham-exposed animals, maintained under the same environmental conditions, served as controls. Specific absorption rates (SAR's) for rats of varying ages were determined by twin-well calorimetry. The average SAR for all rats used in the twin-well calorimetry measurements was calculated to be 2.8 + or - 1.5 mW/g. Between exposures, animals were evaluated using various developmental and biological indices. No difference was observed between 100-MHz-exposed and sham-exposed rats for complete blood counts, mitogen-stimulated response of lymphocytes, frequency of T- and B-lymphocytes, or antibody response to Streptococcus pneumoniae capsular polysaccharide. No mutagenic effect on the sperm cells of rats exposed for over 90 days to 100 MHz was observed using the Dominant Lethal Assay. The mean time to eye opening was significantly accelerated in exposed compared to sham-exposed rats; however, no other significant difference in neutrological development was observed. In rats exposed to 100MHz, significant decreases in the activity of acetylocholinesterase were observed in the striatum and medulla oblongata of 22-day-old rats and in the midbrain of 40-day-old rats but not in 97-day-old animals.