Cultures of isolated mesophyll protoplasts ofBrassica napus L.have shown a positive reaction with the acidic phloroglucinol test for lignin (Wiesner reagent) 30 h after the beginning of the culture period. The reaction was observed in protoplasts and in a very early stage connected with divisions, in which acidic phloroglucinol positive material was primarily deposited like a girdle surrounding the division plane. Brown exudates, which are a serious problem even in young cultures derived from isolated protoplasts, have been secreted into the medium by cells, and also showed a positive reaction. The same staining pattern has been found with toluidine blue 0.