In time course experiments performed in subjects carrying haemoglobin Hasharon and beta-thalassaemia the synthesis of alphaA-, alphaHasharon-, beta- and gamma-globin has been determined. The alpha-globin molecules synthesized in excess were found to be removed from the red cell cytoplasm (phenomenon characteristic of beta-thalassaemia, described by Bargellesi et al, 1968a); in addition the alphaHasharon-globin molecules were removed at a faster rate than normal alpha-globin. The preferential removal of the mutant alpha-globin explains the reduced level of haemoglobin Hasharon found in subjects carrying the gene for beta-thalassaemia (Alberti et al, 1975). Reductions below normal levels of other haemoglobin variants occurring in the presence of the counterpart-globin thalassaemia are probably determined through a similar mechanism.