This study, reported in Nature, suggests that prolonged exposure to low-intensity microwave fields may produce biological effects that are non-thermal. The authors found that the microwave fields induced heat-shock responses in the soil nematode Caenorhabditis elegans. The worms were exposed overnight to continuous-wave microwave radiation at 750 MHz. The calculated SAR was 0.001W/kg. The presence of heat-shock proteins (HSPs) was deduced from measurement of chemicals that act as "reporter products".

The authors present evidence that these responses are non-thermal. Mechanisms for the heat-stress response "could include microwave disruption of the weak bonds that maintain the active folded forms of proteins; enhanced production of reactive oxygen species; or interference with cell-signaling pathways that affect HSP induction". They suggest that "because of the universality of the heat-shock response, a similar non-thermal induction might also occur in human tissues exposed to microwaves, a possibility that needs investigation".