Fourteen Spanish families, containing at least one affected child with cystic fibrosis, were typed for restriction fragment length polymorphisms (RFLPs) by proper pJ3.11, pmet H and pmet D. Nine (64.3%) were fully informative for prenatal diagnosis and carrier detection; four (28.5%) were partially informative and prenatal exclusion of an affected fetus could be carried out in half of pregnancies. One (7.1%) was uninformative for these probes. Allelic frequencies obtained have also been analized, being pJ3.11 probe the most informative in our families.