Physico-chemical properties of intact lysosomes isolated from rat liver tissue were studied using spectrophotometric methods. The lysosomal suspension did not show specific maximal peaks in spectra of light passing through, scattering and absorbance. Stability of the suspension was most suitably evaluated at 520 nm. The rate of lysosomes lysis was distinctly increased at temperature above 37 degrees at pH below 3.0 and above 7.0 as well as in osmotic pressure (pi) exceeding 0.75 MPa. The temperature of phase conversion at 12.5 degrees and 38.5 degrees was calculated from Arrhenius plot. Activating energy of the lysosomes thermolysis was equal to 50, 2 and 18 kcal/mol for solid, mixed and liquid phases of lysosomal membranes, respectively. Additional incubation of the initial lysosomal suspension at 0-4 degrees within 24 hrs led to an increase in osmosis- and acid-stability within all the ranges of pi and pH values studies as well as to decrease of its sensitivity to hypothermia (10-30 degrees) but not to hyperthermia (above 37 degrees). Cadaverine at final concentration 1.0 and 0.1 mM protected lysosomes from thermolysis. Osmotic-resistance, acid-stability and thermotolerance may be used as available dynamic parameters of the particles structure state as well as in evaluation of deteriorating effects of various physicochemical factors in vivo and in vitro.