The aim of the study is to assess what happens to C1-esterase inhibitor that is administered under the skin of subjects with hereditary angioedema. Three different dosing regimens of C1-esterase inhibitor will be assessed. Each subject will be assigned to receive 2 of the 3 dosing regimens, each for 4 weeks. The activity and concentration of C1-esterase inhibitor in the blood will be measured during each 4-week period. The study will also examine how well C1-esterase inhibitor administered under the skin is tolerated by the subjects.