In order to examine the correlation of cytometric DNA ploidy in paraffin-embedded tumour material, a comparison was made of flow (FCM) and image cytometry (ICM); in the case of ICM FEULGEN-stained tissue sections (8-10 microns) and in some cases nuclear suspensions were used. Tumour tissue from seminomas (FCM: n = 50; ICM/section: n = 28), oral squamous carcinomas (FCM: n = 110; ICM/section: n = 50) and adenocarcinomas of the gallbladder (FCM: n = 50; ICM/section: n = 46; ICM/nuclear susp.: n = 40) was studied. The concordance regarding diploid/non-diploid characteristics was 96.5% in the case of seminomas, 87% in oral carcinomas and 100% in gallbladder carcinomas. A statistically significant correlation of DNA indices of FCM with ICM histograms was found in all three organ tumours examined. 6% of oral and up to 18% gallbladder carcinomas, however, could not be evaluated by means of FCM due to poor quality of the histograms (coefficient of variation (CV) > 6%). In the determination of DNA indices and resolution of multiploid stemlines, FCM analysis proved to be superior. Regional intratumoural differences and rare tumour populations were best detected by ICM using sections. Without correction factors being used, these sections did not show any significant deviation of DNA indices from the other methods used. Our study has revealed that in paraffin-embedded tumour material FCM and ICM usually provide well-correlating results, when standardised and controlled preparation and measuring procedures are applied.(ABSTRACT TRUNCATED AT 250 WORDS)