OBJECTIVE To conduct serologic surveillance for Leishmania spp in English foxhounds from a kennel, as well as recipients of blood from these dogs, and determine whether L infantum organisms could be transmitted via blood transfusion. METHODS Serologic prevalence survey. METHODS 120 English foxhounds and 51 dogs of various breeds receiving blood from these donors. METHODS Foxhound blood donors, foxhound nondonors, and nonfoxhound blood recipient dogs were evaluated serologically for Leishmania spp by indirect fluorescent antibody testing. Dogs that received packed RBC (PRBC) transfusions from foxhound donors from mid-1996 through mid-2000 were identified. Furthermore, dogs were serologically evaluated if they had received fresh frozen plasma (FFP) transfusions in 1999 and 2000 from seropositive foxhound blood donors. RESULTS Thirty percent of the English Foxhounds were seropositive for Leishmania spp (titer > or = 1:16), although the degree of seropositivity varied considerably during the period. Furthermore, 57 foxhounds had been used as donors from 1996 to 2000, and 342 units of PRBC had been transfused to at least 227 patients. All 25 dogs screened that received PRBC from seronegative foxhound donors tested negative, whereas 3 of 7 dogs that received PRBC from seropositive donors tested positive. All 9 dogs that received FFP from seropositive foxhound donors remained seronegative. CONCLUSIONS To our knowledge, this report documents the first transmission of Leishmania spp by blood transfusion. The use of foxhounds as blood donors may not be advisable in North America.