Significant correlations between certain spectra of atmospherics (spherics) according to Baumer (a.t.B), i.e. naturally occurring electro-magnetic impulses in the range of 4-50 kHz, and several diseases or biological parameters have been published earlier. Now we show that there exists a highly significant negative correlation (r = -0.61, P greater than 0.004) between the occurrence of 28 kHz impulses (a.t.B.) and the in vitro incorporation of thymidine into the nuclear DNA of C6-glioma cells. The positive correlation with the 10 kHz impulses (a.t.B) (r = 0.39), however, is statistically not significant (P greater than 0.055).