We have analyzed 143 unrelated Belgian patients with a positive diagnosis of cystic fibrosis (CF) for mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. An initial screening for 29 CFTR mutations led to mutation identification in 89.9% of the tested chromosomes. Subsequently an extensive analysis of the CFTR gene was performed by denaturating gradient gel electrophoresis (DGGE) in those patients with at least one unknown mutation after preliminary screening. In addition to 10 previously reported mutations we identified 2 new mutations 186-2A-->G and E588V. A third new mutation 1671insTATCA was identified during routine screening for DeltaF508. Two mutations were detected with a higher frequency than expected: 3272-26A-->G, which is the second most common mutation after DeltaF508 in our CF population with a frequency of 3.8%, and L927P (2.4%). The clinical data is presented for the mutations 186-2A-->G, E588V, 3272-26A-->G and L927P. The mutation data are useful for the Belgian population to supplement the initial screening set of mutations.