Approximately 300–350 bases of sequence information can be obtained directly from λgt1 1 inserts employing the procedure described in this chapter. This chapter presents an autoradiogram of a sequence obtained from a λgt 11 recombinant clone. Two loadings of the sequencing reactions can be visualized on the gel, the leftmost four lanes containing the first load. The relatively large size of the λgt 11 vector (44 kb) probably causes minor difficulties encountered in the sequencing procedure, such as increased background in all gel lanes. This could be due to host–nucleic acid contamination, damaged template DNA, or to the increased opportunity for spurious priming on the large vector. Primers should routinely be checked for homology to vector sequences before use, especially at the 3' end of the oligonucleotide where polymerization is initiated.