Two sets of plaque-forming λ transducing phages have been isolated which carry parts of the tryptophan (trp) and lactose (lac) operons. The λp trp-lac set of phages carry the trp and lac operons in the same orientation connected by deletions which enter the lac regulatory region from the i side. These deletions start at various sites in or near the trp operon and end either late in the lac i gene, within the promoter, between the promoter and the operator, within the operator, between the operator and the z gene, or very early in the z gene. Starting with one particular trp-lac fusion strain, a series of transducing phages were isolated which contain varying portions of the trp operon extending from the trp A gene towards the trp operator. The other set of phages, which are designated λp trp/lac, carry trp and lac in opposing orientations. These λp trp/lac phages contain deletions which remove all of the lac structural genes and end between the operator and the z gene.