Production of alpha-fetoprotein (AFP) was determined in single cells of hepatoma McA-RH7777 and in the clones of their progeny. To elucidate the heritability of this trait in a series of cell generations, a variety of local hemolysis in gel was devised. According to the method the cells and red cells conjugated with protein A were placed on the polylysine covered surface and layered with agarose gel containing antibodies. AFP production by single cells was determined from the formation of plaques--areas of red cell hemolysis. The cells forming the plaques (+AFP) and not forming them (-AFP) were distinguished and their reproduction was followed up. After 7-14 days the cells were fixed and stained by the immunoperoxidase technique with antibodies to AFP. High efficacy of the cloning has been demonstrated for both +AFP- and -AFP-cells (69 and 71%). Negative cells preserved their phenotype more frequently, producing homogenous negative clones, whereas +AFP cells gave "negative" clones in 1/3 of the cases. Both cells gave mixed clones in a small percentage of the cases. At present the AFP trait in these cells is being studied by recloning.