Cystic Fibrosis (CF) is the most common and severe autosomal recessive disease 
in Caucasian populations, with an incidence of 1 in 2500 live births. It is 
characterized by a generalized disturbance in exocrine glands and it is caused 
by over one thousand mutations at the cystic fibrosis conductance regulator gene 
(CFTR) mapped at 7q31. AF508 is the most frequent mutation worldwide and it 
consists in a deletion of the codon that encodes fenilalanine at the 508 
protein's position. The aim of this study was to determine the frequency of the 
delta F508 mutation in Venezuelan patients with CF using the Polymerase Chain 
Reaction (PCR). We studied thirty patients of twenty eight families who were 
diagnosed with CF based on their clinical features and sweat chloride level > 60 
mEq/l in two determinations. Detection of the mutation was performed from the 
amplification of a 98 pair of bases (pb) CF gene segment which contains the 
codon that encodes fenilalanine in the 508 position by PCR. This PCR product is 
absent in those who have the mutation. The delta F508 allelic frequency was 
26.79%, distributed in six homozygous and seven compound heterozygote delta 
F508/X. The reminder mutations (no delta F508) represent 73.21%. The delta F508 
frequency in our sample is less than the reported in European countries. On the 
other hand, a delta F508 frequency highly heterogeneous has been observed in 
Latin-American countries. This variation results from mixed populations with a 
different genetic background influenced by external migration and CF molecular 
alterations, which exists in the analyzed populations. In this study, the delta 
F508 mutation comes mainly from grandparents (79.41%) who were born in 
Mediterranean countries and Colombia, while the no delta F508 mutations come 
from grandparents who were born in Venezuela (79.27%) and Colombia (17.07%).