The paper deals with the taxonomy of cancerogens according to the mechanism of their effect and detection of carcinogenity. It also informs about the most frequently presented carcinogens in relation to particular organs and about reported professional tumours in the Czech Republic. Tumours represented 2.5 % of reported occupational diseases in the Czech Republic between 1999 and 2003, whereas tumours of lung (199), mesotheliomas (15) and tumours of a urine bladder (11) were the most frequent ones. The possibilities of prevention are briefly outlined alongside.

        Key words: tumours, carcinogens, initiators, promotors