The applicability and the present limitations of the laser microprobe mass analyser LAMMA -500 as an instrument for the structural analysis of higher molecular weight, non-volatile, bio-organic compounds (less than or equal to 2000 u) were investigated. For this purpose mass spectra of various synthetic and natural compounds representing cell wall components of Gram-negative bacteria, e.g. phospholipids and lipid A-like molecules were studied. In several cases these spectra exhibited relatively simple and interpretable patterns with a prominent quasi-molecular ion originating from alkali attachment. For one group of the compounds studied--synthetic lipid A-like molecules containing a phosphate moiety--the spectra were rather complicated and lacked pronounced quasi-molecular peaks. Possible reasons for this observation are discussed.