Abstract: continuous flow analysis system measures the cholesterol distribution among different lipoprotein classes in a blood sample. A blood plasma sample is separated into different lipoprotein classes by single vertical spin density gradient ultracentrifugation. The sample is then introduced in a continuous succession into a reagent stream which flows continuously through a detector. A sensor detects the end of the sample in a sample stream before it is introduced into said reagent stream. A wash solution is introduced into the sample stream in response to detection of the end of said sample. The wash solution back flows through the sample stream into the sample container to wash any residue and/or air bubbles from the sample stream. After a predetermined time period, the sample stream is closed and the process is repeated for the next sample.