To investigate the incidence of 13q14 deletion [del (13q14)] in chronic lymphocytic leukemia (CLL), Spectrum Orange labeled sequence-specific DNA probes D13S319 and D13S25 for 13q14 and interphase fluorescence in situ hybridization (I-FISH) were applied to detect del (13q14) in 24 patients with B-CLL. The results showed that among 24 patients, 10 patients (41.7%) had del (13q14) with D13S319, 11 patients (45.8%) had del (13q14) with D13S25, and 9 patients (37.5%) had del (13q14) with both D13S319 and D13S25. The incidence of del (13q14) in Binet stage A, B, C was 4/7 (57.1%), 3/7 (42.9%) and 5/10 (50.0%) respectively by D13S319 probe detection, and there was no significant difference between three Binet stages (P>0.05). It is concluded that the region of loss at 13q14 locates between D13S319 and D13S25 in CLL, and the I-FISH is a rapid and sensitive technique for analysis of del (13q14) in CLL.