Hepatitis is an infection and inflammation of the liver, and hepatitis B is the most common strain found in drug users. About 1 in 20 of those infected develop chronic disease with a high risk of cirrhosis and liver cancer. The transmission routes for hepatitis B virus are the same as for HIV, but the hepatitis B virus is more infectious. Those mainly at risk include injecting drug users, those whose immune systems are impaired, those engaging in unsafe sex practices, those in intimate contact with chronic carriers, and infants born to carriers. Preventive measures involve safer drug use and safer sex practices, but effective vaccination also is available though expensive. New treatments in the form of anti-viral drugs are being developed. 3 figures (Author abstract modified)