Abstract: A n alkaline single cell gel elect ropho resis assay has been standardised by w h ich m u tagen sen sit ivity and DNA repair capacity (DRC) can be m easu red in cryop reserved peripheral b lood lymphocytes fo llow ing induct ion and repair of DNA dam age induced by b leom ycin. In an ongo ing case2con t ro l study, w e have app lied th is assay to Caucasian pat ien t s w ith non2sm all cell lung cancer (n= 160) and respect ive tumo r2f ree ho sp ital con t ro ls (n= 180). A f ter adju stm en t fo r age, gender and smok ing statu s, w e found a stat ist ically sign if ican t associat ion be2 tw een increased m u tagen sen sit ivity (OR = 4, 95%C I 2. 227. 4) , reduced DRC (OR = 2. 1, 95%C I 1. 124) and elevated risk fo r non2sm all cell lung cancer. Bo th m arkers em erged as independen t cancer risk facto rs. W e have also tested w hether cryop resevat ion inf luences m u tagen sen sit ivity and DRC. W hen f resh lymphocytes w ere compared w ith cryop reserved samp les, there w as no sign if ican t inf luence of cryop reservat ion t im e (1 to 371 days) neither on the amoun t of b leom ycin2induced dam age no r on the individualDRC as repeatedlym easu red in fou r b lood dono rs. W e conclude: ( i) in comparison to estab lished cytogenet ic test s, ou r new assay ism uch less t im e con sum ing, and m u tagen sen sit ivity and DRC can be assessed as independen t endpo in t s. ( ii) becau se it al2 low s sto rage of cryop reserved lymphocyte samp les, ou r assay is su itab le as a too l in mo lecu lar ep idem io logy. P ro spect ive studies to iden t ify h igh risk individuals and elucidat ion of the underlying m echan ism s fo r disease su scep t ib ility are now w arran ted.