Interaction between radiation and Adriamycin damage reduced the width of the shoulder of the X-ray survival curve. This effect was found to persist for at least 24 hr after Adriamycin treatment. Adriamycin did not affect radiosensitivity. The drug did not suppress repair of radiation damage when cells were treated either before two-dose fractionation or with the drug present between X-ray exposures. Adriamycin is unique in that its major effect on radiation response is to reduce the survival curve shoulder without affecting two-dose recovery. It is suggested that Adriamycin and radiation produce independent classes of damage that are expressed mutually for killing, with regard to the registration of sublethal radiation damage, but that repair of the latter is unaffected by Adriamycin.

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Supported by USPHS Grant CA-12662 and Training Grant CA-05237 from the National Cancer Institute, NIH.

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