A detailed investigation of the iron(III)-cyanide and iron(III)-hydroxide systems has been made in NaClO4 media at 25 degreesC, using combined UV-vis spectrophotometric and pH-potentiometric titrations. For the Fe(III)/OH- system, use of low total Fe(III) concentrations (less than or equal to 10 muM) and a wide pH range (0 less than or equal to pH less than or equal to 12.7) enabled detection of six mononuclear complexes, corresponding to the following equilibria: Fe3+(aq) + rH(2)O <----> Fe(OH)(r)((3-r)+)(aq) + rH(+)(aq), where r = 1-6 with stability constants (log *beta(1r)) of -2.66, -7.0, -12.5, -20.7, -30.8, and -43.4, respectively, at I = 1 M (NaClO4). It was also found to be possible to measure, for the first time, stability constants for most of the following equilibria: Fe3+(aq) + qCN(-)(aq) <----> Fe(CN)(q)((3-q)+)(aq), despite a plethora of complicating factors. Values of log beta(1q) = 8.5, 15.8, 23.1, and 38.8 were obtained at I = 1.0 M (NaClO4) for q = 1-3 and 6, respectively. No reliable evidence could be obtained for the intermediate (q = 4 or 5) complexes. Similar results were obtained for both systems at I = 0.5 M(NaClO4). Spectra for the individual mononuclear complexes detected for Fe(III) with OH- and CN- are reported. Attempted measurements on the Fe(II)/CN- system were unsuccessful, but values of log beta(16)(Fe(CN)(6)(4-)) = 31.8 and log beta(15)(Fe(CN)(5)(3-)) approximate to 24 were estimated from well established electrode potential and other data.