We evaluated the analytical performance of a newly developed electrochemiluminescence immunoassay for everolimus and sirolimus compared to that of liquid chromatography-tandem mass spectrometry (LC-MS/MS). According to Clinical and Laboratory Standards Institute guidelines, the analytical performance including precision, recovery, linearity, and carryover was evaluated. For correlation evaluation, the results of Elecsys® analysis of everolimus and sirolimus were compared with those of LC-MS/MS using 120 samples from patients treated with everolimus or sirolimus. The within-run and total imprecision values were as follows: 2.3%-4.5% and 4.5%-6.4% for the everolimus assay; 3.3%-4.8% and 4.7%-8.1% for the sirolimus assay, respectively. The measured concentration was linear over the range of 0.718-27.585 ng/mL for everolimus analysis and 0.789-26.880 ng/mL for sirolimus analysis (all R2 > 0.99). Recovery was 93.5%-105.5% for the everolimus assay and 99.2%-109.1% for the sirolimus assay (except lowest levels). Carryover was -1.09% for the everolimus assay and -0.12% for the sirolimus assay. The results of the two chemiluminescence immunoassays showed acceptable correlations with those of LC-MS/MS (R = 0.9585 and R = 0.9799, respectively). The two immunoassays showed slightly proportional biases compared to LC-MS/MS. Elecsys® Everolimus and Sirolimus assays showed acceptable analytical performance in precision, linearity, and correlation compared to LC-MS/MS These methods can be adopted in the clinical laboratory for rapid therapeutic drug monitoring of patients who require treatment with immunosuppressants. © 2019 The Authors. Journal of Clinical Laboratory Analysis Published by Wiley Periodicals, Inc.