Some three-component phenolic block copolymers have been prepared from the following three monomeric units: p-amino-phenol, p-chlorophenol, and p-creso1. Homopolymerization of these monomers has been done with formaldehyde in the presence of acid catalyst. The homopolymer samples were then condensed together with stoichiometric quantities of formaldehyde and acid catalyst. Several samples of the copolymers were also prepared by changing the composition of the feed during homopolymerization. Composition, DP, and the average number of a particular monomeric uhit in a block of a copolymer chain has been deduced from electrometric titration curves of the copolymers in nonaqueous media.