Abstract
A family (H-J pedigree) segregating for the A and F alleles at cholinesterase locus 1 is described. Apparent anomalous results led to the recognition of a new allele (E1j) also segregating in the family. The data are consistent with the hypothesis that the the E1j causes reduction of 'usual' (E1u) molecules by about 66%. Whether this is because of retarded synthesis or accelerated degradation of serum cholinesterase remains to be determined.