KEYWORDS CLASSIFICATION: analysis;Antigens,CD;Antigens,Differentiation,T-Lymphocyte;biosynthesis;blood;Biology;cytology;Dose-Response Relationship,Radiation;Electromagnetic Fields;Flow Cytometry;Germany;Heat-Shock Proteins;HSP70 Heat-Shock Proteins;Humans;Immunophenotyping;Lymphocytes;mechanisms of carcinogenesis;metabolism;Monocytes;pharmacology;physiology;Proteins;radiation effects;Radio Waves;Reactive Oxygen Species;Research;Tetradecanoylphorbol Acetate;Umbilical Cord;Umbilical Veins; A r i ΰ l ;biomarkers of exposure & effect: validation. The aim of this study is to investigate if 1,800 MHz radiofrequency electromagnetic fields (RF-EMF) can induce reactive oxygen species (ROS) release and/or changes in heat shock protein 70 (Hsp70) expression in human blood cells, using different exposure and co-exposure conditions. Human umbilical cord blood-derived monocytes and lymphocytes were used to examine ROS release after exposure to continuous wave or different GSM signals (GSM-DTX and GSM-Talk) at 2 W/kg for 30 or 45 min of continuous or intermittent (5 min ON/5 min OFF) exposure. The cells were exposed to incubator conditions, to sham, to RF-EMF, or to chemicals in parallel. Cell stimulation with the phorbol ester phorbol-12-myristate-13-acetate (PMA; 1 microM) was used as positive control for ROS release. To investigate the effects on Hsp70 expression, the human monocytes were exposed to the GSM-DTX signal at 2 W/kg for 45 min, or to heat treatment (42 degrees C) as positive control. ROS production and Hsp70 expression were determined by flow cytometric analysis. The data were compared to sham and/or to control values and the statistical analysis was performed by the Student's t-test (P