THE liver is undoubtedly the major site of glucuronide synthesis in the mammal1,2, but varying degrees of glucuronide synthesizing activity have also been reported for other tissues. These include the kidney1,2, intestine3, cartilage4 and granulation tissue5, although the findings of different workers have not always been in agreement. The only specific investigation of this nature which we have been able to find applied to such activity in skin is that of Zini6, who reported that isolated rat skin possesses ‘some’ glucuronide synthesizing activity with o-aminophenol as substrate. No quantitative details are given, but the assumption is that the level of activity falls far below that of other tissues in which significant activity was observed. Evidence from another field, however, would suggest that the glucuronide synthesizing ability of skin may be by no means insignificant and indeed may play an important part in the detoxification of foreign substances at that site. Thus it is now well confirmed that the carcinogenic hydrocarbon, 3 : 4-benzpyrene, is metabolized in mouse skin both in vivo 7–9 and in vitro 10 to yield a water-soluble polar derivative designated as BPX 2 (ref. 7). Subsequent work by one of us (K. H. H.) has shown this metabolic fraction to consist of a mixture of glucuronide conjugated benzpyrenols11. The analogous sulphate conjugated fraction11, on the other hand, has not so far been detected within the skin, and this has led one of us (G. C.) to suggest that the formation of this complex (BPX 1 is divorced from the carcinogenic response elicited by 3 : 4-benzpyrene at this site8. It was of importance, therefore, to re-examine the conjugating ability of mouse skin in the light of this evidence.