The European wild rabbit (Oryctolagus cuniculus) is the main prey for several endangered species and an important game species in the Iberian Peninsula. However, over the last several decades 2 diseases, myxomatosis and rabbit hemorrhagic disease (RHD), have contributed to a decline in rabbit populations. In Spain, vaccination campaigns against both diseases and the translocation of vaccinated rabbits are frequently used in projects aimed at stimulating the recovery of wild populations. We estimated which factors related to body condition were associated with successful immunization by vaccination. In 191 adult wild rabbits, we calculated a body-mass index and analyzed a number of biochemical parameters and antibody concentrations before and after vaccination. Results showed that, respectively, 81 and 84% of initially seronegative rabbits seroconverted after vaccination against myxomatosis and RHD. We also found that RHD antibody concentrations after vaccination were positively associated with total protein concentrations at the moment of vaccination in all rabbits, whereas RHD antibody concentrations were negatively related to the creatinine concentration at the end of our study for initially seronegative rabbits. Our results suggested that in wild rabbits vaccination was an effective way of increasing antibody concentrations and, thus, of fighting myxomatosis and RHD, although the intensity of the immune response was conditioned by the body condition of individual rabbits. Consequently, rabbit translocations could be improved by avoiding the translocation of individuals with poor body condition and by improving vaccination protocols. In addition, success rates in mass vaccination programs carried out in free-living wild populations may be increased if the body condition of individuals is evaluated before vaccination campaigns are carried out.