A 52-year-old man with mild diabetes and acute stem cell leukaemia developed an orbitofacial mucormycosis. Cultures showed the fungus to be Rhizopus oryzae. Vigorous treatment with amphotericin B and other bactericidal and bacteriostatic antibiotics for a concurrent sepsis failed to suppress the infections, and the patient died. On post-mortem examination characteristic haematoxylin-staining, broad, aseptate fungal hyphae were found in the right eye, orbit, and lung. A striking and unusual feature of this case is the presence of brightly birefringent crystals within the severely degenerated eye. These were found by histochemical staining and x-ray diffraction studies to be calcium salts of fatty acids, apparently liberated from necrotic adipose tissue of the orbit.