Mixtures of deuterium-labeled trans-8, cis-8 and cis-9-octadecenoic acids (8t-18:1, 8c-18:1, 9c-18:1) were fed as triglycerides (TG) to two adult male subjects. Blood samples were collected sequentially over a 48-hour period. Plasma and lipoprotein lipids were separated by thin layer chromatography and analyzed by gas chromatography-mass spectroscopy. Results indicate (i) absorption of the 8t- and 8c-18:1 isomers were similar to 9c-18:1; (ii) the 8t-18:1 isomer was cleared approximately 30% faster than 9c-18:1 from plasma TG; (iii) cholesterol ester samples contained 8.4 times less 8t-18:1 than 9c-18:1; (iv) incorporation at the 1-acyl phosphatidylcholine (PC) position was higher for 8t-18:1 and 8c-18:1 (2.2 and 1.7 times) than for 9c-18:1; and (v) discrimination at the 2-acyl PC position was 4.6-fold against 8t-18:1 and 1.3-fold against 8c-18:1 compared with 9c-18:1. Discrimination against uptake of the delta-8 isomers in both neutral and phospholipid classes suggests that both 8t- and 8c-18:1 may be preferentially oxidized relative to 9c-18:1. Except for triglycerides, data for each of the lipid classes from total plasma and individual lipoprotein samples were similar. These data indicate that differences for incorporation and turnover of the 8t- and 8c-18:1 isomers relative to 9c-18:1 are not substantially influenced by the lipoprotein classes. The maximum isotopic enrichment detected in the chylomicron triglycerides fractions was 60%, which indicates that a substantial amount of endogenous triglycerides was mobilized during absorption of the deuterated fats.