In previous studies, sinus secretions have been analysed concerning pO2, pCO2 and pH. In this study the energy metabolism in the maxillary sinus mucosa and secretion was studied in 33 New Zealand White rabbits. In freeze-dried samples, glucose and lactate were analysed by enzymatic assays and ATP by HPLC. In the purulent sinusitis, lactate concentration in the mucosa was 5.67 mmol X kg-1 w.w. and significantly higher than in the control sinus. Also in the non-purulent sinusitis, lactate was increased in the mucosa. The lactate concentrations in the secretion were 9.8 and 8.4 mmol X kg-1 w.w. in purulent and non-purulent secretions respectively and are probably the result of a diffusion from the mucosal cells and of leukocyte metabolism. A reduced ATP content, with increases in ADP and AMP, in the sinus mucosa of the purulent sinusitis suggests a relative energy depletion which could result in impaired epithelial function.