Blood will be drawn from study participants and their parents. Two tablespoons of blood (one tablespoon in small children) will be drawn by standard techniques from a vein in the arm. Whenever possible, blood samples for this study will be collected at the same time that it is done for medically needed blood tests. This blood will be used to extract DNA and to establish cell lines that we will store as a permanent source of DNA. We will compare your clinical symptoms with your DNA to see if additional genes that affect CF symptoms can be found. Some serum and plasma will be stored for later testing, as additional knowledge becomes available. Any tests done in the future with your stored blood samples or your DNA will only be to answer questions about genes for CF.