The adenomatous polyposis coli (APC) gene was investigated in Swedish patients with familial adenomatous polyposis (FAP). A combination of analyses including single stranded conformation polymorphism (SSCP), heteroduplex (HD), protein truncation test (PTT) and direct sequencing was used to enable optimal mutation detection. Three novel mutations in the gene were identified, i.e. nt2644C- > T (giving an Arg876Stop mutation), nt4025del173 (leading to premature truncation of the protein at codon 1337) and nt3526insG (giving truncation at codon 1178). In addition, one previously described mutation, i.e. the 5-bp-deletion nt3942del5(AAAGA) in codon 1309 (giving a premature termination of the protein at codon 1314) was detected. All four mutations were located in the 5'-half of exon 15. The two latter mutations were associated with the CHRPE (congenital hypertrophy of retina pigment epithelium) phenotype (CHRPE was not examined in the other two cases). The patients with mutations in codon 1309 and 1336 had a more severe FAP phenotype.