The Drosophila genome encodes a total of nine Toll and related proteins. The immune and developmental functions of Toll and 18Wheeler (18W) have been analyzed extensively, while the in vivo functions of the other Toll‐related proteins require further investigation. We performed transgenic experiments and found that overexpression of Toll‐related genes caused different extents of lethality and developmental defects. Moreover, 18w, Toll‐6, Toll‐7 and Toll‐8 often caused related phenotypic changes, consistent with the idea that these four genes have more conserved molecular structure and thus may regulate similar processes in vivo. Deletion alleles of Toll‐6, Toll‐7 and Toll‐8 were generated by targeted homologous recombination or P element excision. These mutant alleles were viable, fertile, and had no detectable defect in the inducible expression of antimicrobial peptide genes except for the Toll‐8 mutant had some defects in leg development. The expression of 18w, Toll‐7 and Toll‐8 mRNA showed wide and overlapping patterns in imaginal discs and the 18w, Toll‐8 double and Toll‐7, Toll‐8 double mutants showed substantially increased lethality. Overall our results suggest that some of the Toll‐related proteins, such as 18W, Toll‐7 and Toll‐8, may have redundant functions in regulating developmental processes.