Summary—The infraciliary lattice (ICL) is the innermost cortical cytoskeletal network ofParamecium. Its meshes which run around the proximal end of basal bodies form a continuous contractile network beneath the cell surface. We had previously shown that the network, which could be recovered in a contracted form and selectively solubilized by EGTA from an ICL‐enriched cell fraction, was principally composed of 23–24 kDa polypeptides cross‐reacting with antibodies raised against the 22 kDa Ca2+‐binding proteins of the ecto‐endoplasmic boundary (EEB), a contractile cytoskeletal network of another ciliateIsotricha prostoma. We show here 1) that the ICL also comprises a 220 kDa polypeptide; 2) that the 23–24 kDa polypeptides are resolved in 2D gels into 11 spots of acidic pI, 7 of which are both Ca2+‐binding and cross‐reacting with the anti EEB polypeptides; 3) that the network displays a high Ca2+‐affinity as the treshold for solubilization/co‐precipitation of both high and low MW polypeptides is around 10−8M free Ca2+; 4) thatin vivocontraction of the network occurs upon physiological increase of internal calcium concentration. The likely phylogenetic relationships of the 23–24 kDa ICL polypeptides with the calmodulin related family of Ca2+‐modulated polypeptides and the functions of the ICL in cell contractility and Ca