Abstract
Forty-one faecal samples from infectious-hepatitis patients and their contacts were investigated for the presence of hepatitis-A-associated viral particles. Of these, 16 gave a positive result by immune electronmicroscopy or caesium-chloride density-gradient centrifugation. The latter method proved invaluable in detecting small numbers of virus particles. The particles found had buoyant density of 1-34-1-35 and a size range of 21-28 nm. Epidemiological evidence suggested that they might be the causative agent of hepatitis A.