Abstract: Mo st of the chem icals classif ied by the In ternat ionalA gency fo r Research on Cancer ( IARC) as hum an carcinogen s are m u tagen ic acro ss test system s, cf. www. epa. govög apdb < h t tp: ööwww. epa. govögapdb> and induce tumo rs at m u lt ip le sites in roden t species. They are therefo re readity detected in sho rt term test s fo r genet ic and related effect s (GRE) , in an im al carcinogenesis b ioassays and in hum an mon ito ring studies. Carcino2 gen s that are no t geno tox icm ay be studied u sing new tox icogenom ic app roaches asw ill be discu ssed. A Chem i2 cal Effect s in B io logical System s (CEBS) database is p lanned by the N at ional Cen ter fo r Tox icogenom ics to con2 tain info rm at ion on such compounds. The 1992 P ream b le to the IARCMonograph s p rovides exp licit gu idelines fo r including GRE in carcinogen icity evaluat ion s. In sub sequen tMonograph s GRE and o ther relevan t data have inf luenced the overall classif icat ion of at least 20 chem icals. Fo r examp le, the genet ic act ivity p rof ile of ethy2 lene ox ide (EO ) show s clear evidence of m u tagen icity in hum an s. EO con sisten t ly induces som at ic cell m u ta2 t ion s in roden t s in vivo, and gene m u tat ion, ch romo som al aberrat ion s, and SCEs in vit ro. There is suff icien t evidence of EO carcinogen icity in roden t s and lim ited evidence in hum an s. Th is, coup led w ith the compelling GRE that suppo rt a m u tagen icm echan ism of act ion, p romp ted the IARC to upgrade EO to a know n hum an car2 cinogen. IARC recen t ly reevaluated 1, 32bu tadiene (BD) as a p robab le hum an carcinogen. Bu tadiene is carcino2 gen ic in m ice and to a lesser degree in rat s. It is bo th m u tagen ic and clastogen ic in num erou s roden t studies, es2 pecially in m ice. Po sit ive resu lt s repo rted in th ree of eleven hum an ep idem io logical studies have indicated that BD may induce gene andöo r ch romo som alm u tat ion s in humans in vivo. We have review ed the GRE data for 1,32bu tadiene and fo r the o ther IARC p robab le and po ssib le hum an carcinogen sw ith hum an environm en tal exposu re. Th is assessm en t of the overall GRE fo r these agen t s, part icu larly tho sew ith po sit ive hum an in vivo data,undersco res the concern fo r adequate p ro tect ion of expo sed hum an s. Th is is an ab st ract of a p ropo sed p resentat ion and does no t necessarily ref lect EPA o r N IEHS po licy.