In an attempt to achieve maximal skin-test positivity to leprosin A in children of leprosy patients living in Baba Baghi Leprosy Sanatorium in Iranian Azerbaijan, two new vaccines have been employed. Children without scars of previous BCG and without response to leprosin A were given a vaccine containing 10(8) viable units of BCG Glaxo plus 10(7) killed Mycobacterium vaccae per dose (vaccine B). Children with BCG Pasteur (Teheran) scars but without response to leprosin A were given a vaccine containing 10(8) killed M. vaccae alone (vaccine D). Eight years later skin testing was repeated, and both new vaccines were found to have significantly increased the numbers of children responding to leprosin A above the level that would have been expected had they received BCG Pasteur alone. This increase was due in large part to increases in the proportions of individuals responding to group i (common mycobacterial) antigens, and known as category 1 responders. The use of suspensions of killed M. vaccae in conjunction with BCG may represent a considerable advance in inducing protection from multibacillary leprosy in close contacts of leprosy patients if leprosin A positivity is truly a correlate of protective immunity. A comparison, using the same criteria, with the other proposed vaccines for leprosy would be very interesting.