Experimental butters with a high content of trans-18 : 1 fatty acids and/or cis-9,trans-11-18 : 2 (rumenic acid; RA) were fed to thirty-six New Zealand White rabbits to investigate their effects on adipose tissue (AT) and liver lipogenic activities. Animals received one of three atherogenic (0.2 % cholesterol) diets containing 12 % butter with either a standard fatty acid composition (rich in saturated fatty acids), rich in trans-10-18 : 1 (T10 diet) or in trans-11-18 : 1 plus RA (T11+ RA diet) for 6 or 12 weeks. The ingestion of butters rich in trans fatty acids and/or RA for 6 weeks had little or no effect on liver and AT lipogenesis. The ingestion for 12 weeks of butter rich in T11+ RA decreased perirenal AT weight, lipogenic enzyme and lipoprotein lipase activities, without affecting liver lipid concentration or lipogenic activities except for a decrease in glycerol-3-phosphate dehydrogenase activity. Similar trends, but of a lower magnitude, were observed in rabbits fed the T10 diet for 12 weeks. Ingestion of the T10 or T11+ RA diets for 6 or 12 weeks had no significant effect on plasma metabolites and hormones except for glucose which increased at 6 weeks in the T10 group. Plasma leptin concentration was positively correlated with AT weight but did not differ between the three diets. In conclusion, the supply of butters rich in either T10 or T11+ RA in an atherogenic diet for 12 weeks decreased rabbit AT lipogenesis, with a more marked effect of the T11+RA diet, but had no effect on liver lipogenesis.