Fluorescent and haptenized, monofunctionally binding platinum compounds are increasingly used for chemically labeling nucleic acids for hybridization detection purposes. Here we analyze in detail the effect of labeling density of the cyanin-3 and -5 platinum DNA adducts on fluorescence and thermal stability. We also analyzed the kinetics of the reaction of the cyanin platinum compounds with DNA. The data provided are important for the design of optimal platinum DNA labeling and hybridization conditions for fluorescence hybridization applications.