We present new and published isotopic data on brachiopod shells from the Urals and Moscow Basin to explore paleoclimate, global change, and chemostratigraphy in the Carboniferous. A total of 134 shells were analyzed from the Askyn, Sokol, Zilim, and Chussovaya sections in the Urals. The most important feature of this record is a sharp increase in 5*bO and 513C at the Serpukhovian-Bashkirian boundary. A Mid-Carboniferous increase had been reported for Moscow Basin and North American sections, but the timing had never been so well constrained. This shift bears witness to the transition from greenhouse to icehouse climate in the Carboniferous. The magnitude of the 6180 and 5bC shifts in the Urals (Askyn section) appears exaggerated because of anomalously low Serpukhovian values. Using the S180 increase recorded in North American and Moscow Basin sections as conservative estimates, this shift implies an ice sheet at least the size of modem glaciers, and perhaps a lowering of tropical temperature several degrees. The simultaneous increase in 613C provides evidence that cooling was promoted by increased burial of organic carbon. These 5lsO and 5 3C shifts appear global and should be useful as chronostrati-graphic markers for the Serpukhovian-Bashkirian boundary. A mid-Kasimovian 6,|50 and 5s 'C minimum in the Moscow Basin may represent a wann interval in the otherwise icehouse Late Carboniferous. Future investigations will test the global nature of this and other isotopic events.