Eleven pediatric acute lymphoid leukemia patients were investigated for chromosomal aneuploidy by interphase cytogenetics using chromosome specific (peri)centromeric probes for all the somatic and sex chromosomes. Results were compared with metaphase cytogenetic and flow cytometric derived DNA aneuploidy data. Experiments performed on normal human cells using chromosome specific (peri)centromeric probes indicated that disomy could be recognized in a range of 89.1+/-2.7% (12.9)-96.8+/-0.2% (0.9) for the somatic chromosomes and in 98.1+/-0.4% (1.3) for the sex chromosomes. Using the cutoff level of the mean false monosomy and trisomy in the control cells +2 S.D., chromosome loss or gain for the somatic chromosomes could be revealed beyond a clonal ratio of 3.6-13.2% and 1.1-6.8%, respectively. The same value for the sex chromosomes was 3.5% and 0%, respectively. In 5 of 11 patients the leukemic cells proved to be diploid with all three methods at both gross DNA and chromosome levels. Interphase cytogenetics revealed chromosome loss or gain in all of the remaining six patients, however, the metaphase analysis indicated numerical aberration in only two patients. In one of them only the increased chromosome number could have been detected without identifying the chromosomes involved and in the other one the two methods indicated trisomy for a different chromosome. Flow cytometric data showed aneuploidy in three of the six aneuploid leukemia patients. The results suggest that interphase cytogenetics might be more accurate compared with flow cytometry and metaphase analysis to reveal aneuploidy.