Comparison of the effects of ethidium bromide and of ethidium bromide-deoxyribonucleic acid complex in fibroblasts cultivated in vitro.

Chick embryo fibroblasts cultivated in vitro were treated with ethidium bromide (E.B.) or with DNA-E.B. complex (DNA-E.B.). E.B. (5 mug/ml) provokes morphological alterations and cell death, inhibits DNA synthesis and mitotic activity. DNA-E.B. (E.B. 5 mug/ml) is less toxic to the fibroblasts as far as cell structure, DNA synthesis and mitotic activity are concerned. DNA alone has no apparent effect on the fibroblasts. As shown by fluorescence microscopy, the lower toxicity of DNA-E.B. seems to be related to its mode of penetration into the cells.