Solid tumours have an elevated interstitial fluid pressure (IFP) due to the lack of normal lymphatics, increased permeability of tumour vasculature and an expanding cell population within a potentially limited space. This elevated IFP has been proposed to be an important barrier to the delivery of drugs and marcromolecules. We have demonstrated that local hyperthermia (4 h, 41.8 degrees C) is capable of significantly enhancing the uptake of radiolabelled monoclonal antibodies (mAbs) in D-54 MG glioma xenografts grown subcutaneously in athymic mice. To determine if this increased uptake was attributable to alterations in the tumour IFP, pressure measurements using the wick-in-needle technique were made in tumours after hyperthermia treatment. These pressure measurements were taken at various time points from 4 to 90 h following the initiation of the hyperthermia and compared with pressures taken concurrently in untreated tumours. In addition, pressures were measured following a 2 h, 41.8 degrees C hyperthermia treatment, a protocol which does not result in elevated uptake of radiolabeled mAbs. No significant differences were seen at any time point in IFP measured in the tumours receiving either hyperthermia treatment when compared with untreated tumours. Thus, we conclude that the mechanism by which this hyperthermia regimen enhances mAb uptake in this human glioma xenograft model is not due to alternations in tumour IFP.