Resumo. ABSTRACT This research aimed to evaluate the influence of removing the diaphragm on the quality of the preservative treatment of bamboo culms of Dendrocalamus giganteus and Bambusa vulgaris submitted to sap displacement method. The bamboos were collected in clumps in Alegre and Jerônimo Monteiro, south of Espírito Santo state, Brazil. The stems were sectioned in culms of 2.0 m in length. One part of the culms had the diaphragm removed while in the other they were kept unbroken. The culms were treated in soutions of 1% and 3% of active ingredients (a.i.) of copper, chromated copper borate (CCB). The culms were kept in the solution for 5, 10 and 15 days. The preservative treatment quality was evaluated by means of penetration and retention of CCB in culms. There was greater penetration of copper and boron at the base of the culms, the removing of the diaphragm provided greater movement of the solution in the culms and the retention was, for most treatment conditions, below than the one recommended by Brazilian standards for wood preservative treatment.