The nucleotide sequence of a secondary attachment site for bacteriophage lambda was determined in a region near the rrnB gene at 88 min on the E. coli chromosome. The sequence has a 8 base pair interrupted homology GCT TTTTA to the common core of the primary attachment site (attB) and the corresponding phage sequence (attP). The site of crossover during integration lies probably between nucleotides -3 and +1. The flanking regions have no obvious homology to the arms of either attP or attB.