Ca-uptake by embryonal chick tibia in short-term culture is herewith used as an empirical model to probe the coupling of electromagnetic signals with biological processes. Tibiae from 8- to 10-day-old chick embryos were incubated 60 to 120 minutes in media of given composition at 37.5±0.5°C in the presence of 45Ca, either inside or outside a very low frequency pulsating electromagnetic field. Ca-uptake by the chick tibia rudiment was best determined by 45Ca counting in aliquots of the culture medium. The field produced an increase in Ca-uptake only in the presence of sufficient quantities of bicarbonate, which was also the most effective of the ions to bring about Ca-uptake outside the field (bicarbonate > phosphate > chloride > acetate). Pharmacologic agents, as ethanol, Mg2+, and NaF, stimulated the positive effect of the field on Ca-uptake, but only in the presence of bicarbonate. The magnitude of the effect was also dependent on the characteristics of the induced electromagnetic signal, whereby the dose-response curves had peaks at certain signal amplitudes. No molecular mechanisms have been as yet identified for the observed electromagnetic effects. However, because of the passivity of non-living systems, it is clearly the Ca-uptake by living tissue that is being modified by the pulsating electromagnetic field. Probable candidates in the electromagnetic coupling that results in an increased Ca-uptake may have to be found in the membrane processes of active ion transport and related phenomena.