The effects of different sample treatments on the X-ray powder-diffraction patterns of Salmonella minnesota R595 deep rough mutant bacterial lipopolysaccharides (LPS) were investigated. Samples were obtained by slow evaporation of aqueous solutions or suspensions of sodium, lithium and natural salt form lipids. Samples were treated by hydration in moist air, heating to 60 degrees C and heating plus hydration. While after heating of samples no changes in diffraction patterns were observed, other treatments resulted in the improvement of peak intensities and sharpness of reflections. Heating plus hydration gave the most significant effects. For one natural salt form LPS sample the treatments resulted in almost doubling of the number of observable : reflections with the highest order found at 2 theta = 36 degrees. It is discussed that the effects of treatments are most probably related to perfection of the lateral and the stacking order in the samples, rather than an improved mosaic spread. The simplicity of our sample treatment:, make them suitable fur application to other than lipopolpsaccharide samples, especially for samples prepared by the Langmuir-Blodgett method.