The proliferative potential and DNA ploidy in 203 brain tumours (27 astrocytomas grade I, 37 grade II, 80 grade III, and 59 grade IV) were investigated using bromodeoxyuridine (BrdUrd) incorporation and flow cytometry. One to three tumour samples from each patient were incubated in vitro for one hour at 37 degrees C with bromodeoxyuridine (BrdUrd) using the high preasure oxygen method. After incubation, fixation and staining, the cell preparations were analysed by flow cytometry. The percentage of BrdUrd-labelled cells (BrdUrd Labelling Index, BrdUrdLI), the predicted potential doubling time (predTpot) and the total DNA content were evaluated. The percentage of unlabelled S-phase cells (SPF) and proliferative index (PI, the percentage of cells in S + G2 phases) were also estimated. DNA aneuploidy was found in 61.1% of high-grade (III-IV) and 50.0% of low-grade (I-II) astrocytomas. The tumours showed variability in the BrdUrdLI values which ranged from 0.2 to 15.8%. Significantly higher mean value for BrdUrdLI was shown in grade III-IV astrocytomas (3.4%), than in grade I-II astrocytomas (1.5%), p = 0.0068. Also significantly shorter mean predTpot was shown in high grade III-IV astrocytomas (28 days) than in low grade I-II tumours (51 days), p = 0.0096. However, no relationship was shown between other cell proliferation parameters and histological grade. The mean intratumoral variability calculated on the basis of BrdUrdLI values on 2-3 samples from each tumour amounted to 31.2% +/- SD 15.9%.