Broccoli (Brassica oleraceae L. var. Italica cv. `Premium Crop') plants grown in perlite were supplied with nutrient solutions containing three levels of added boron (0.04 (severely deficient), 0.08 (moderately deficient) or 0.80 (normal) mg L-1). These treatments produced plants exhibiting either obvious (0.04 mg L-1) or no visual boron deficiency symptoms (0.08 and 0.80 mg L-1). At horticultural maturity, cross sections were taken in the upper and mid stem regions. The specimens were mounted on slides after being processed through a biological staining series. Boron availability was found to be correlated with the progressive internal deterioration of the stem which was observed histologically. An examination of staining patterns indicated that possibly a lignification process accompanies and contributes to hollow stem development. We have previously noted an increase in phenolic compounds and fiber content of broccoli produced under boron deficient conditions. The histological evidence of lignification further substantiates that boron deficiency induces changes in cell wall structure which may contribute to the development of hollow stem.