Assessment of radiation doses through measurement of dicentric chromosomes may be difficult due to the inability of damaged cells to reach mitosis. After high-dose exposures, premature chromosome condensation (PCC) has become an important method in biodosimetry. PCC can be induced upon fusion with mitotic cells, or by treatment with chemicals such as calyculin A or okadaic acid. Several different cytogenetic endpoints have been measured with chemically induced PCC, e.g., via scoring of extra chromosome pieces or ring chromosomes. The dose–effect curves published with chemically induced PCC show differences in their coefficients and in the distribution of rings among cells. Here we present a study with calyculin A to induce PCC in peripheral blood lymphocytes irradiated at nine different doses of γ-rays up to 20 Gy. Colcemid was also added in order to observe metaphase cells. During microscopical analysis the chromosome aberrations observed in the different cell-cycle phases (G2/M-PCC, M/A-PCC and M cells) were recorded. The proportion of G2/M-PCC cells was predominant from 3 to 20 Gy, M cells decreased above 1 Gy and M/A-PCC cells remained constant at all doses and showed the highest frequencies of PCC rings. Depending on the cell-cycle phase there was a difference in the linear coefficients in the dose–effect curves of extra fragments and rings. Poisson distribution among PCC rings was observed after calyculin A + colcemid treatment, facilitating the use of this methodology also for partial body exposures to high doses. This has been tested with two simulated partial exposures to 6 and 12 Gy. The estimated doses in the irradiated fraction were very close to the real dose, indicating the usefulness of this methodology. © 2013 Elsevier B.V.