No pullulanase activity could be detected in maltose-grown cultures of 11 different strains of Escherichia coli. Neither these strains, nor 40 other strains of the same species would grow on pullulan, while all of them grew on maltose and some were shown to grow on maltotriose the exclusive product of pullulanase action on pullulan. These results are in contradiction with those reported last year in this journal by Palmer, Wober and Whelan. On the other hand pullulanase activity could be detected, as reported by Bender and Wallenfels in 1966, in two strains of Aerobacter aerogenes.Pullulanase is an amylopectin and glycogen debranching enzyme produced by certain bacteria such as Aerobacter aerogenes and Streptococcus mitis [i-31. Its name is derived from that of its most convenient substrate, pullulan, a linear polysaccharide produced by the fungus Pullularia pullulans, and composed of about 480 maltotriose units linked by 01-1,6 glycosidic bonds [4].In a recent paper [5] Palmer et al. report the occurrence of a pullulanase in Escherichia coli strain ML. They claim that the enzyme is induced during growth on maltose, and that it is located in the outer membrane of the bacterial envelope. When pregrown on maltose, E. coli ML is reported to grow on pullulan. To us, these observations were of considerable interest, mainly because recent results from our laboratory demonstrate that a maltose-induced protein of the outer membrane constitutes the receptor for bacteriophage lambda [6]. Although apparently not involved in the metabolism of maltose, this protein is coded by a gene located in one of the maltose operons [7]. The possibility existed that pullulanase was the phage receptor. Unfortunately phage lambda does not adsorb onto E. coli ML cells (our unpublished results) and no pullulanase activity can be found in E. coli K12, the standard host for bacteriophage lambda (Palmer and Wober, personal communication). Still we proceeded to look for a strain of E . coli which might a t the same time have a pullulanase and adsorb phage lambda. The result of this search, summarized in this paper, is that we were unable to find physiological or biochemical evidence for the occurrence of a pullulanase in any strain of E. coli, including E. coli strain ML.