There is considerable controversy surrounding the biological effects of 
radiofrequency (RF) fields, as emitted by mobile phones. Previous work from our 
laboratory has shown no effect related to the exposure of 1.9 GHz 
pulse-modulated RF fields on the expression of 22,000 genes in a human 
glioblastoma-derived cell-line (U87MG) at 6 h following a 4 h RF field exposure 
period. As a follow-up to this study, we have now examined the effect of RF 
field exposure on the possible expression of late onset genes in U87MG cells 
after a 24 h RF exposure period. In addition, a human monocyte-derived cell-line 
(Mono-Mac-6, MM6) was exposed to intermittent (5 min ON, 10 min OFF) RF fields 
for 6 h and then gene expression was assessed immediately after exposure and at 
18 h postexposure. Both cell lines were exposed to 1.9 GHz pulse-modulated RF 
fields for 6 or 24 h at specific absorption rates (SARs) of 0.1-10.0 W/kg. In 
support of our previous results, we found no evidence that nonthermal RF field 
exposure could alter gene expression in either cultured U87MG or MM6 cells, 
relative to nonirradiated control groups. However, exposure of both cell-lines 
to heat-shock conditions (43 degrees C for 1 h) caused an alteration in the 
expression of a number of well-characterized heat-shock proteins.