In vitro studies provide evidence that support and EM field induced thermal mechanism for immune effects. When proper control of culture temperatures has been achieved during in vitro exposure to EM fields, no alterations have been observed for a variety of immune cell functions. There is conflicting evidence for effects on lymphocytes exposed in vitro to amplitude modulated EM fields at 60Hz. More work is needed to determine if there exists a possible interaction between low frequency modulated EM fields and the immune system. At present, however, there is no convincing evidence from in vivo and in vitro animal studies that EM fields adversely alter the immune system at levels found in the ambient environment.