In order to explore the value of interphase fluorescence in situ hybridization 
(FISH) in the detection of partial deletion of the long arm of chromosome 20 
(20q(-)) in patients with myelodysplastic syndrome (MDS), spectrum Green 
fluorescein directly labeled yeast artificial chromosome (YAC) clone 912C3 which 
spans the breakpoint cluster region in band 20q12 was used as probes to perform 
interphase FISH on the marrow cells from 52 cases of MDS and 5 normal controls. 
200 to 300 cells were scored for each case and cases which had cells with a 
green hybridization signal>7.16% were defined as 20q(-) positive. The results of 
FISH were compared with those of conventional cytogenetics (CC) assay. The 
results showed that among 52 cases of MDS, 7 (13.5%) cases were positive by 
FISH, however, of which, 4 cases were positive and the other 3 cases were 
negative by CC assay. It is concluded that YAC912C3 and interphase FISH 
providing a powerful technique in the detection of 20q(-) in MDS is an important 
complement to CC assay.