The disturbed fluorescence response of the coenzyme NADH in biological
tissues has been observed. The oscillation features of the NADH fluor
escence decay (excitation at 337.1 nm, fluorescence at 460 +/- 20 nm)
for isolated cell membrane structures are different from that for cyto
plasm. An analysis of the experimental data with the method of the sys
tem theory proves the nonlinear behavior of the fluorescence decay.