In this regular issue of Reviews of Physiology the first contribution by Warth and Bleich is on K+ Channels and Colonic Function, the second by Offermanns on Mammalian G-Protein Function in vivo: New Insights Through Altered Expression, and the third contribution by Tenenholz et al. (including one editor of the series) on Structural Determinants of Scorpion Toxin Affinity: The Charybdotoxin (alpha-KTX) Family of K+-channel Blocking Peptides. TOC:R. Warth/M. Bleich: K+ channels and colonic function.-S. Offermanns: Mammalian G-protein function in vivo: New insights through altered gene expression.- T.C. Tenenholz, K.C. Klenk, D.R. Matteson, M.P.Blaustein, and D.J. Weber: Structural determinants of scorpion toxin affinity: the Charybdotoxin (alpha-KTX) family of K+ channel blocking peptides.