In a pilot-like study, six human cell types, immortalized cell lines and primary cells, were exposed to 900 and 1800 MHz and analyzed on whole-genome cDNA arrays. NB69 neuroblastoma cells, T lymphocytes, and CHME5 microglial cells did not show significant changes in gene expression. In EA.hy926 endothelial cells, U937 lymphoblastoma cells, and HL-60 leukemia cells between 12 and 34 up- or down-regulated genes were found. Analysis of the affected gene families does not point towards a stress response. However, following microwave exposure, some human cells might react with an increase in expression of genes encoding ribosomal proteins and therefore up-regulating the cellular metabolism.