Problems in the interpretation of FLM data of externally irradiated cell populations are mainly due to the interference of radiation effects with radiotoxic effects originating from incorporated [3H]thymidine. These problems were investigated using L-929 cells flash labelled in vitro with [3H]thymidine (30 min, 0.3 microCi/ml, 40 Ci/mM) and irradiated with 2 Gy of 200 kV X-rays; the fractions of labelled mitoses and the index of labelled and of unlabelled mitoses were determined. The results showed that the FLM is not an adequate parameter to quantify the early cell kinetic changes in irradiated cell populations.
