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potentiation of this effect by physical or chemical agents. Exponentially grow- ing cultures of NCTC clone of L cells were used in these experiments. Cells were exposed to cytostatic drugs (m-[di(2~hloroethyl)amino]-L-phenylala. nine and adriamycin) at 37 or 42°C. We also investigated the effect of hyper- thermia before or after cytostatic treatment. At different post.treatment incubation periods cells were harvested for chromosomal preparations using the conventional air<lrying method.

The results show that the extent of chromosomal aberrations is dose and time dependent. The frequency of the chromosomal aberrations is significantly potentiated after different sequences of heat (42°C) and drug exposure.

This research was part ly supported by IAEA, Vienna, Contract No. 1677/R4/RB.

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

Effect of cytostatics on the survival of mammalian cells growing in vitro

The present investigations were carried out to evaluate the response of mam- malian cells t o t h e treatment with the cytostatic drugs PTC and VM-26 at nor- mal (37°C) or hyperthermic {42°C) condition. These drugs possess a high thera- peutic effectiveness on various types of malignant tumors. The effects of drug exposure and inhibitors of repair processes on the survival of NCTC clone of L cells were studied by the method of colony-forming units. Mammalian cells treated with these cytostatics accumulate sublethal damage which is evidenced by the presence of a shoulder on the survival curves. When the cells were exposed to these drugs at elevated temperature (42°C) the potentiation of kill- ing effect was observed. From the shape of the survival curves it is evident that hyperthermia suppresses repair processes. This is shown by a reduction of the shoulder and a steeper slope resp. The suppression of the repair system is also investigated by exposing cells to the inhibitor of repair processes during post- treatment incubation.

This research was par t ly supported by IAEA, Vienna, Contract No. 1677/R3/RB.

Kubiak, R., Institute of Systematic and Experimental Zoology, Polish Acad- emy of Sciences, Cracow (Poland)

SCE induced by rubratoxin B

Chinese hamster embryonal fibroblasts were exposed to different concentra- tions of rubratoxin B in the presence of serum and without the addition of mixed function oxidases ("$9 mix"). After a 1,h treatment with lower concen- trations (10 and 20 /~g/ml) an increase of SCE was seen. The number of SCEs