Roger Tsien, who was a frequent guest in Lindau, passed away on August 24th, last year. His work on Ca++ chelators, Ca-indicator dyes, probes for cyclic AMP, and fluorescent proteins changed the whole field of functional studies on the cellular level. His synthesis of BAPTA-type compounds provided the first Ca++ chelator, which had little pH-dependence, but high Ca++/Mg++ selectivity and fast binding kinetics. BAPTA effects, in comparison to those of the slow Ca++ binder EGTA, turned out to be the tools of choice, when estimating the tightness of coupling between Ca++-selective ion channels and Ca++ sensors during the Ca++ triggering of synaptic neurotransmitter release. Fluorescent derivatives of BAPTA, developed by Roger Tsien in the mid-80s rapidly became the favorite Ca++-indicators for the quantitative measurement of rapid Ca++ changes in nerve muscle, endocrine and almost any other cell type. We used these indicators extensively for studying Ca++ signals in adrenal chromaffin cells and glutamatergic nerve terminals. Last not least, the availability of genetically encoded fluorescent proteins greatly enhanced the usefulness of genetic modifications for the study of cellular signaling.