Simple, rapid and cost-effective methods are sought for measuring immunoglobulin G (IgG) concentrations in bovine serum, which can be applied for diagnosis of failure of transfer of passive immunity (FTPI). The aim of the present study was to investigate the potential use of Fourier-transform infrared (FTIR) spectroscopy, with partial least squares (PLS) regression, to measure IgG concentrations in bovine serum. Serum samples collected from calves and adult cows were tested in parallel by radial immunodiffusion (RID) assay and FTIR spectroscopy. The sample IgG concentrations obtained by the RID method were linked to pre-processed spectra and divided into two sets: a combined set and a test set. The combined set was used for building a calibration model, while the test set was used to assess the predictive ability of the calibration model, resulting in a root mean squared error of prediction (RMSEP) of 307.5-mg/dL.The concordance correlations between the IgG measured by RID and predicted by FTIR spectroscopy were 0.96 and 0.93 for the combined and test data sets, respectively. Analysis of the data using the Bland-Altman method did not show any evidence of systematic bias between FTIR spectroscopy and RID methods for measurement of IgG. The clinical applicability of FTIR spectroscopy for diagnosis of FTPI was evaluated using the entire data set and showed a sensitivity of 0.91 and specificity of 0.96, using RID as the reference standard. The FTIR spectroscopy method, described in the present study, demonstrates potential as a rapid and reagent-free tool for quantification of IgG in bovine serum, as an aid to diagnosis of FTPI in calves.