The possible risks of radio-frequency electromagnetic fields for the human body is a growing concern for our society. We have previously shown that weak pulsed microwaves give rise to a significant leakage of albumin through the blood-brain barrier. In this study we investigated whether a pathologic leakage across the blood-brain barrier might be combined with damage to the neurons. Three groups each of eight rats were exposed for 2 hr to Global System for Mobile Communications (GSM) mobile phone electromagnetic fields of different strengths. We found highly significant (p < 0.002) evidence for neuronal damage in the cortex, hippocampus, and basal ganglia in the brains of exposed rats. Key words: blood-brain barrier, central nervous system, microwaves, mobile phones, neuronal damage, rats. Environ Health Perspect 111:881-883 (2003). doi:10.1289/ehp.6039 available via http://dx.doi.org/