[en] Determination of the biological effectiveness for internally deposited α- and β-emitting radioactive materials using a number of endpoints is needed to make meaningful risk estimates for man. Late-occurring biological effects were studied in Chinese hamsters injected with ²³⁹Pu, ¹⁴⁴Ce or ⁹⁰Sr citrate. Pu-239 is an α emitter which localizes in liver and bone, whereas ¹⁴⁴Ce and ⁹⁰Sr are β emitters which localize in liver and bone, and in bone, respectively. Biological alterations on the cellular, organ and organism level can be used in determining the relative effectiveness of α and β radiation in producing these endpoints. Significant life shortening was induced by all three radionuclides and was considered in evaluating time-related incidence of bone and liver neoplasms. Osteosarcomas were seen in animals injected with 1.0 μCi ⁹⁰Sr citrate and 0.002 μCi ²³⁹Pu citrate/g body weight, while liver tumours including hemangiosarcomas, fibrosarcomas and hepatocellular neoplasms, were seen after injection of 0.25 μCi ¹⁴⁴Ce citrate and 0.002 μCi ²³⁹Pu citrate/g body weight. Comparisons of bone and liver tumourincidences with cumulative radiation dose were made to derive quality factors for tumour production. In both cases, the derived factors (3.6 for bone tumours and 7.4 for liver tumours) were lower than the figure of 10 generally accepted for comparing α and β radiation. The factor derived from comparison of chromosome damage in liver cells was higher (15), indicating that other factors are involved between damage at the cellular level and final tumour production, and that direct correlations of genetic damage and tumorigenicity are hazardous. (author)