The objective of Biological Dosimetry is its applicability in radioprotection, quantifying the dose received in individuals who have been exposed to ionizing radiation. For this raison, the analysis of the frequency of chromosome aberrations present in first division metaphases from stimulated lymphocytes is accepted as being the reliable. However, in proliferating cells there are several checkpoints that prevent damaged cells to pass through, and heavily damaged cells show an impossibility to reach mitosis. Concretely the chemically induced premature chromosome condensation by Calyculin-A in combination with Colcemid it is possible to score in the same slide cells that were in interphase and in metaphase. The aim is to determine if Calyculin-A has any effect in the dicentric yield observed in metaphase cells. Peripheral blood samples were irradiated at 1, 4, and 10 Gy of γ-rays and cultured for 48 hours. Colcemid was added 24 or 2 hours before harvesting, and for comparisons cultures were also treated with of Calyculin-A at the last hour. For the three doses the proportion of M cells was always higher after 24 hours in presence of Colcemid than after 2 hours. When the frequencies of dicentrics were compared, there were no major differences between cultures where only Colcemid was used (2 or 24 hours) and those where the Calyculin-A treatment was also done. The results indicate that when PCC-CA is used if metaphase cells are considered similar dose-effect curves will be obtained than those obtained using the conventional mitotic arrest with Colcemid.