Therapeutic drug monitoring of cyclosporine (CsA) blood values in renal transplant recipients is of extreme importance; hence, finding contributing factors in this issue is relevant. In this study, we aimed to evaluate potential associations of some characteristics of the recipients including their human leukocyte antigen haplotypes with their drug bioavailability.616 patients who had a valid HLA typing result concomitant with other demographic data in our local data registry were consecutively selected. We extracted their HLA typing, age, gender, weight, cause of renal failure, first measured CsA trough level (C0) and concomitantly measured creatinine, CsA administered dosage, time duration from transplantation, routine laboratory test results, panel reactive antibodies percentage, and immunosuppression type. Bivariate and multivariate linear regressions were employed to evaluate associations of these factors with blood C0 values.64.5% of patients were male. Mean age at transplantation was 40.7+/-15.8. Mean first measured C0 was 271+/-178 ng/ml. Analysis showed that the only factors which had independent association with C0 were age at transplantation, dose/weight ratio and HLA-B27.genetic factors as well as age of patients are two founded factors in this study which are recommended to be considered in monitoring drug administration in organ transplant recipients.