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aerobic and hypoxic conditions, The analysis of chromosomal aberrations has shown that increased toxicity of this drug in hypoxia is due to the damage induced in genetic material. The significant increase in the number of aberrant mitoses, with the appearance of stable structural lesions, was detected in hy- poxic samples after 6 h of incubation in the presence of 10 mM metronidazole. In aerobic samples the chromosomal damage remained at the control level. Sim- ilar results were obtained with tinidazole, a drug which belongs, as does me- tronidazole, to nitroimidazole derivatives.

It can be concluded that nitroaromatic drugs form a specific group of po- tential mutagenesis, which nee d the metabolic activation connected to hypoxia for their expression.

46 Lj. Kosti6, O. Djordjevid and G. Brki6, Institute of Nuclear Sciences "Boris Kidri~", Radiobiological Laboratory, Beograd (Yugoslavia)

Effects of drugs on m a m m a l i a n cel ls growing in vitro

The aim of these investigations was the comparative study of the effects induced by chemical agents on the reproductive capacity of mammalian cells growing in vitro. Two agents have been used throughout these investigations: Peptichemio (PTC) and adriamycin.

The experiments are carried out with NCTC clone of L cells. In logarithmic phase of growth cells were treated with different concentrations of the drugs at normal (37 ° C) and elevated temperature (42 ° C). As a parameter of survival the colony-forming ability of cells was used. The results show that the survival of L cells depends on drug concentration and exposure time of cells to the drug at 37°C. Having in mind that both of these drugs are successfully used in chemo- therapy of malignant diseases the potentiation of this effect by hyperthermia could be very useful. The data show that hyperthermia (42°C) does increase killing effect of mammalian cells treated either with PTC or adriamycin. The obtained survival curves might indicate that hyperthermia + PTC act on the inhibition of repair processes, while in case of hyperthermia + adriamycin the pronounced synergism was observed.

47 M. Osmak, A. Ferle-Vidovi6 and D. Petrovi6, Institute "Ruder Bo~kovi6", Zagreb (Yugoslavia)

Biological effects of crude oil destillate o n cells in cu l ture

In examination of various cellular properties of C3Hf and L929 mouse cells after the treatment with crude oil destillate there were not found unambiguous changes which would indicate that the treated cells have adopted new elements of malignant behaviour. The treated cells have not demonstrated either decreased contact inhibition, or significant increased ability of tumour develop-