This study was undertaken to evaluate the influence of hyperventilation (HV) as a test on the image contrast of brain glial tumors in enhanced magnetic resonance (MR) imaging. HV was performed for 2 min (30 breaths/min) before intravenous injection of Gd-DTPA (Magnevist), Schering AG, Germany, in a dose of 0.1 mmol/kg. A total of 19 patients with glial tumors of the brain were examined. After the functional test, the image contrast of tumor tissue was compared with tumor contrast after the standard enhanced MR imaging. Nineteen patients with brain tumors were assessed. The tumor types were histologically verified in all cases (nine malignancy degree I-II astrocytomas, six malignancy degree III astrocytomas, three ependymomas, one malignant oligodendroglioma). MRI was performed on a Magnetom 42 SP-1.0 T. There was an increase in the image contrast of degree I-II astrocytomas neither after the standard enhanced MRI nor after it in the presence of HV. On the contrary, in 2 cases there was an opposite effect--the tumor contrast decrease after the functional test. Ependymomas showed patterns of increases in contrast intensity from 10 to 13% as compared with the enhanced standard MRI in all cases. In these conditions the intrinsic structure and boundaries of tumors became more distinguished. Cases with malignant astrocytomas and oligodendroglioma had contrast enhancement increases as well. It is concluded that in cases with degree I-II astrocytomas, the use of HV does not improve the visualization of lesions. In ependymomas and anaplastic astrocytomas, HV aids in more significantly assessing the intrinsic structure and the extent of tumorigenesis and it may be useful as a functional test to assess the anaplastic extent of glial tumors of the brain and as a procedure enabling the contrast agent to be used in smaller dosages.