Comparative optical study of bio°uids (serum, urine, hemodialysate) by concentration change of endogenous visible°uorescence substance (VFS) has been carried out. Bio°uids were collected from chronic kidney diseases (CKD) patients (Pts) as well as from healthy controls (HCs). Excitation/emission spectra are similar for all samples of bio°uids di®ering only in intensity, which is higher for CKD Pts. Strong similarity enables the study of given bio°uids from a united physical platform, proposed earlier, i.e., as nanoparticles approach. Speci¯c spectral redistribution of visible°uorescence (VF) intensity as a result of dilution is revealed. The concentration change of VFS by dilution of samples manifests in nonlinear dependences in the scales \VF intensity-concentration" for serum and urine and in perfect linearity for hemodialysate (HD). The latter fact can be used in monitoring of hemodialysis procedure.