Previously, we reported that plasma half-lives of a drug incorporated in lipid emulsions prepared with soybean oil (SO), a long-chain triglyceride, and hydrogenated castor oils (HCOs) (SO/HCOs) were markedly longer, while those as SO/polyoxyethylene sorbitan esters (SO/PSs) were similar, compared to that as SO/egg yolk phosphatides (SO/EYP) [J. Pharm. Pharmacol. 54 (2002) 1357; J. Drug Target. 11 (2003) 37]. In the present study, lipid emulsions were prepared with Miglyol 812 (MO), a medium-chain triglyceride, and HCOs, and the kinetics of the incorporated drug, menatetrenone, were examined. The plasma half-lives and the liver uptake of menatetrenone as MO/polyoxyethylene-(10)-hydrogenated castor oils (MO/HCO10s) were similar to and larger than those as MO/EYP, respectively. On the other hand, the plasma half-lives and liver uptake of menatetrenone as MO/polyoxyethylene-(20)-hydrogenated castor oils (MO/HCO20s) or MO/polyoxyethylene-(60)-hydrogenated castor oils (MO/HCO60s) were markedly longer and lower than those as MO/EYP, respectively. The pretreatment of dextran sulfate 500,000, a reticuloendothelial system suppressor, raised the plasma concentration and inhibited liver uptake of menatetrenone as MO/HCO10, but not for MO/HCO20. These findings suggest that the minimum number of oxyethylene units within HCOs for the prolonged plasma circulation of menatetrenone was 20 for MO/HCOs, similarly to SO/HCOs.