Radiation Chemistry Department, Institute of Nuclear Medicine & Allied Sciences, Brig. S. K. Mazumdar Road. Delhi- 110 054. India E-mail: snu@inmas.org Manuscript received 27 July 2004, revised 5 October 2004, accepted 8 October 2004 Present review has focused on the ionising radiation induced biomarkers. These biomarkers were different biochemicals, biopolymers, enzymes, single cells, chromosomes etc. Ionising radiation dose is varied from few eGy to 50 Gy to bring about detectable changes in all the systems mentioned. For biochemical markers — their source, dose range, effect that is brought about by radiation dose have been mentioned. For enzymes also, their source, dose at which enzyme activity alters have been mentioned. For biopolymers — their origin, dose range within which response is linear at a particular dose rate have been mentioned. For single cells by microgel electrophoresis technique lysis condition, electrophoresis condition, measurement parameters and dose range have been mentioned. Relatively recently different types of chromosomal aberrations, lymphocyte — dicentric assay, different types of DNA damages and DNA mutations, gene expression and protein expression changes etc. as induced by ionising radiation exposure have been used as biodosimeters. These all are in the eGy dose range. In recent times their importance have increased due to their medical and military utility and for accident dosimetry purposes.