The fasting plasma lipids, lipoproteins, and apolipoproteins were evaluated in 5 subjects with undetectable levels of the plasma protein β2-glycoprotein I (apolipoprotein H). Family studies confirmed an autosomal co-dominant inheritance pattern for the concentrations of apo H. The total lack of this protein is rare and less than 0.3% of clinic patients demonstrated levels undetectable by radial immunodiffusion. Plasma lipoprotein evaluation in these subjects with β2-glycoprotein I absence by analytical ultracentrifugation and compositional analysis demonstrated low concentrations of HDL(2b) and HDL3. More striking, however, was the lack of a consistent marked effect on the plasma lipoproteins as is found in other apolipoprotein deficiency states. We conclude that the lack of apolipoprotein H does not result in a significant perturbation of normal lipoprotein metabolism as reflected by analysis of fasting plasma lipoproteins. Further study is required to evaluate the role of this glycoprotein in the metabolism of triglyceride-rich lipoproteins.