Cambial stem chips containing intact cambium between xylem and phloem, or with the phloem layer removed, were cut from the main stem axis of four-year-old Eucalyptus globulus during the winter and grown under controlled environmental conditions for seven weeks on fully defined culture media . Light microscopy revealed that tyloses were induced in sapwood vessels in the region adjacent to the cambium within these stem chips. When incubated in autoclaved double-distilled water (control medium) tyloses were produced in 3.7% and 4.7% of vessels in chips with the phloem layer intact and removed, respectively. When non-hormonal ingredients were included, tyloses developed in 69.5% and 76.1% of vessels in chips with the phloem layer intact and removed, respectively. Addition of 1.0 mg l-1 of l-naphthalene acetic acid (NAA, a synthetic auxin) to the medium had a slight, but significant, inhibitory effect on tylosis formation.