Objective: Histological assessment of tissue damage and localisation of bacteria in autopsy materials of patients who died of septic shock. Design: Prospective observational study. Setting: General and paediatric intensive care units, Tartu University Hospitals and Institute of Anatomy, Tartu University. Patients: 2 patients, who died of septic shock; 1 patient, who died of trauma. Measurements and results: Tissue samples of different organs (lungs, heart, spleen, pancreas, liver, adrenals, kidneys and brain) were studied for the presence of bacteria and for the local inflammatory reaction with light microscopy. Bacteria (cocci) were found in the capillaries and tissues of both septic shock patients, but not in the control patient. Capillary dilatation, oedema, stasis and cell death, but no polymorphonuclear infiltration, were seen around the foci of bacterial invasion. Conclusions: Massive penetration of bacteria into all tissues without significant polymorphonuclear infiltration may take place in severe septic shock.