L929 mouse fibroblast cells were exposed to 835 MHz TDMA and CW at 2.5 W/kg in a TEM cell. After 8 hours of TDMA exposure, maximal induction was observed. No effects were observed, however, following 8 hours of CW exposure or RF which was amplitude modulated with random speech (ie: coherent signal modulation necessary for ODC induction). In another study, L929 fibroblasts were exposed to 835-MHz microwaves (AM either uniformly at 60 Hz or by a burst at 50 Hz as a signal from a Motorola MicroTAC phone [DAMPS]) at an average of 2.5 W/kg in a TEM cell. In some experiments, ELF (30 to 100 Hz electromagnetic noise with rms amplitudes of up to 10 uT) was superimposed on the microwave fields from Helmholtz coils built around the TEM cell. Statistically significant increases of ODC activity (exposed to sham ratio of 1.9, p<0.0001) were observed with AM microwave exposure as long as the ELF noise was maintained below 0.5 uT. When the superimposed noise was increased to above 0.5 uT, the microwave-induced increases in ODC activity were progressively inhibited, with full suppression at 2 uT for uniform 60 Hz modulated and 5 uT for DAMPS signals. IN a related study, L929 fibroblasts were exposed to 835-MHz microwaves (CW, AM at 16 or 60 Hz, AM with a 50-Hz square wave pulses, AM at a speech frequency, FM with 60 Hz sinusoidal wave, or FM with signals from a TDMA or analog cellular telephone) for 2 to 24 hr in a TEM cell at an average SAR of 2.5 W/kg. CW exposure had only a minimal effect on increasing ODC activity (exposed to sham ratio of 1.3 +/-0.2, p<0.004). AM frequencies modulated at 16, 55, 60, and 65 Hz produced significant increases in ODC activity (exposed to control ratio of 1.5 +/- 0.3 (p<0.012), 1.9 +/- 0.5 (p<0.009), 1.9 +/- 0.4 (p<0.0001), and 2.1 +/- 0.4 (p<0.0011), respectively). AM modulation at 6 and 600 Hz was ineffective. Irradiation with microwaves modulated with the 50-Hz pulsed signal caused an approximate 40% increase in ODC activity. Irradiation with FM-modulated microwaves or microwaves modulated at the speech frequency had no significant effect on ODC activity. Eight-hour exposure to the signal from the digital cell phone (burst-modulated at 50 Hz with a 30% duty cycle) caused a 40% increase in ODC activity (OAR of 1.4 +/- 0.2, p<0.0002). Irradiation with the signal from the analog telephone, which uses a form of FM, had no significant effect on ODC activity.