Background/Aims: APC is inheritable in an autosomal dominant manner and includes both familia) adenomatous polyposis(FAP) and Gardners syndrome(GS). For the presyptomatic diagnosis of APC, several DNA markers on Sq for linkage analysis are now available. A]so, a PCR-based screening method for mutation analysis is available. To evaulate the usefulness of two different presymptomatic diagnostic tests for APC, we performed linkage and mutation analyses, respectively, on both FAP and GS families. Methods: Genomic DNA was extracted from the peripheral lymphocytes from 8 members of affected fami]ies with APC and 5 members with GS. Five micrograms of each DNA was digested with restriction enzyme Msp I, and Southern blotting and hybridization using the probe EF 5.44 were performed. Using PCR with [a- PJ dCTP incorporated for labelling, DNA fragments were amplified by both the DSS82 and tbe DSS346 locus respectively, and identified by ethidium bromide staining after agarose gel electrophoresis. Products of the PCR were loaded on 10% denaturing(8M urea) polyacrylamide gels in TAE buffer, and the reactions visualized by autography. For the detection of germ-line mutations, two different segments of the APC gene were arnplified by the PCR and analyzed by PAGE. Results: All the polymorphic markers, except CA repeat marker YN5.64 in GS family, are not informative in both FAP and GS fami]ies. Although CA repeat marker YN5.64 is informative in GS family, presymptomatic diagnosis can not be made with certainty because this one is an index family with spontaneous mutation. Using the two systems for the detection of re]atively common germ-line mutations, presymptomatic diagnosis can be made only in GS family. Conclusions: Linkage analysis and systems for the detection of germ-line mutations using PCR, although useful in some situations, could benefit a minority of kindreds with adenomatous polyposis coli. (Korean J Gastroenterol 1996; 28:185 - 197)