Synchrotron radiation-Fourier transform infrared (SR-FTIR) microscopy coupled with multivariate data analysis was used as an independent modality to monitor the cellular bystander effect. Single, living prostate cancer PC-3 cells were irradiated with various numbers of protons, ranging from 50-2,000, with an energy of either 1 or 2 MeV using a proton microprobe. SR-FTIR spectra of cells, fixed after exposure to protons and nonirradiated neighboring cells (bystander cells), were recorded. Spectral differences were observed in both the directly targeted and bystander cells and included changes in the DNA backbone and nucleic bases, along with changes in the protein secondary structure. Principal component analysis (PCA) was used to investigate the variance in the entire data set. The percentage of bystander cells relative to the applied number of protons with two different energies was calculated. Of all the applied quantities, the dose of 400 protons at 2 MeV was found to be the most effective for causing significant macromolecular perturbation in bystander PC-3 cells.