Base excision repair can be measured in human lymphocytes by a variety of techniques, the most convenient of which are probably in vitro assays of the activity of a cell extract on a DNA substrate containing specific lesions such as 8-oxoguanine. Inter-individual variation in base excision repair ranges from about 3-fold to 10-fold in different studies. Repair has been variously reported to decline or to increase with the age of the individual. Few studies of environmental or occupational exposure and repair have been carried out, but it seems that styrene exposure induces base excision repair activity. In several nutritional intervention trials, with kiwifruit, coenzyme Q(10) and carrots, a significant enhancement of repair has been noted. Activity of 8-oxoguanine DNA glycosylase is significantly affected by the Ser326Cys polymorphism in hOGG1. In cancer case-control studies, low repair activity is consistently associated with occurrence of the disease.