Eight skin graft donor-recipient pairs were selected by lymphocyte typing for production of HL-A typing antisera. After the second or third skin graft from the same donor, antibodies appeared in the sera of five of the recipients. The antibodies were directed against antigens which seem to be determined by alleles of the LA and 4 sub-loci, and the specificity showed close correlation to the HL-A incompatibility between donor and recipient. By re-immunization with intradermal leucocyte injections, two additional recipients produced antibodies against donor cells. One of these antisera seemed to detect a new HL-A antigen of the 4 sub-locus (called FJH). It is concluded that skin grafting and leucocyte injections is a simple and efficient method for production of HL-A typing antisera of desired specificity. The results also indicate that the remaining alleles of the HL-A system may be identified by antisera obtained by this method.