Cell Biology. In the article “Cloned mammalian neutral sphingomyelinase: Functions in sphingolipid signaling?” by Stefan Tomiuk, Kay Hofmann, Michael Nix, Markus Zumbansen, and Wilhelm Stoffel, which appeared in number 7, March 31, 1998, of Proc. Natl. Acad. Sci. USA (95, 3638–3643), two typographical errors occurred: (i) the two C-terminal lysine residues (KK) of the mouse sequence in Fig. 1 on page 3640 should be omitted. The protein contains 419 amino acid residues ending on alanine as stated on page 3639 and (ii) also on page 3640 (left column, line 13) the text should read: phosphatidylcholine was found to be cleaved by approximately 3% efficiency not 30%.