Four betulin esters of 1,2-diacyloyl-sn-glycero-3-phos-phatidyl acids were synthesized, characterized by NMR spectroscopy and studied for antimicrobial activity against Staphylococcus aureus ATCC 25923. Neither betulin nor betulinic acid nor the synthesized esters showed any microbial effect after 24 h long incubation in Mueller-Hinton substrate at 37 degrees C.