INTRODUCTION
We applied chemical-induced PCC technique to analyze the frequency of chromatid breaks, and the kinetics of rejoining and misrejoining of breaks after high-LET irradiation in G2-phase human cells.

METHODS
Exponential growing human fibroblast cells AG1522 were irradiated with energetic carbon, silicon and iron particles. Immediately following exposure, chromosomes were prematurely condensed by calyculin A then chromatid breaks and exchanges in G2 cells were scored. Chromosomes were also collected using PCC technique after several repair times ranging from 5 to 600 minutes at 37 degrees.

RESULTS
Kinetics of rejoining of chromatid breaks consisted of two exponential components. The number of chromatid breaks decreased rapidly in the first 10 minutes, and then continuously decreased at a slower rate. The repair kinetics was poorly LET dependent. Chromatid exchanges were formed very quickly following irradiation. The frequency of residual breaks for heavy-ions was higher than that for gamma rays. Isochromatid breaks were frequently observed in high-LET irradiated samples.

CONCLUSION
The chemical-induced PCC technique allows chromatid breaks to be analyzed easily, quickly and precisely. Using this technique, the difference in the relative frequency of different types of chromatid aberrations was detected between low and high-LET radiations.