Escherichia coli pel - mutants inhibit the penetration of bacteriophage lambda DNA into the cell. Using P1 mediated cotransduction, we mapped pel - mutations between markers fadD and eda in the interval of minute 40 of the revised E. coli K-12 map. This places pel in the same region as genes kdgR and ptsM. Mutations in kdgR usually do not alter the Pel phenotype, and vice versa. In contrast, about 30% of ptsM - mutants are also pel -, and all pel - mutants isolated are ptsM -. These results suggest that pel and ptsM are one and the same gene. This interpretation would identify the bacterial product required for injection of phage λ DNA as a component of the phosphoenolpyruvate-dependent phosphotransferase system specific for mannose, glucosamine, glucose and fructose. However, the experimental results do not exclude an alternative explanation: that pel and ptsM identify two closely linked genes which would be simulataneously affected at high frequency by a particular mutational event.