This study is an extension of a previously published study on female Pim1 transgenic mice conducted by Repacholi et al. (Radiat. Res. 147, 631-640, 1997) that reported a significant increase in lymphomas after exposure to the same 900 MHz RF signal. A total of 500 mice, with 50 per sex per group, were exposed for 1h/day, 7 days/week for 18-months (pulse width: 0.577 ms; pulse repetition rate: 217 Hz) in plastic tubes similar to those used in inhalation studies to obtain well-defined uniform exposure. The study was conducted blind. The exposure levels were 4, 1.3, 0.44 W/kg. The results of this study do not suggest any effect of 217 Hz-pulsed RF-radiation exposure on the incidence of tumors at any site, and thus the findings of Repacholi et al. were not confirmed. Overall, no effect of RF radiation under the conditions used on the incidence of any neoplastic or non-neoplastic lesion was shown, and thus the study does not provide evidence that RF radiation possesses carcinogenic potential.