The BK-type Ca2+-activated K+ channel has been the subject of increasingly detailed mechanistic study since the first recordings of this channel were obtained more than 25 years ago (Pallotta et al., 1981; Latorre et al., 1982; Magleby, 2003; and references therein). But if you thought that our understanding of the gating of the BK channel and its allosteric regulation by Ca2+ and transmembrane voltage had reached its summit, then once again you would be wrong. In a remarkable display of patch-clamping and kinetic analysis appearing in this issue, the bear is poked once again, with this iteration of analysis constrained by high-resolution Ca2+ dose-response curves, containing data at 22 (!) different [Ca2+]. Here, Sweet and Cox (see p. 491) analyze the two high-affinity Ca2+ binding sites of the BK channel using mutations to selectively disable each site, and obtain definitive results on how the sites behave in isolation and how they might interact with one another in the intact BK channel. A surprising finding is that binding to one of the two binding sites is modulated by transmembrane voltage. This intriguing twist opens possibilities for identifying a structural basis for interactions between the voltage sensor and one of the principal Ca2+ activation sites of the channel.