This thesis examines the factors affecting the stability of chlorhexidine salts (principally gluconate) in dilute aqueous solution (0.001 to O.05%w/v). Such studies are pertinent to the use of chlorhexidine as a preservative in aqueous pharmaceutical products. The introduction details the factors affecting the stability of pharmaceuticals in solution. Published work on the physico-chemical properties of chlorhexidine and structurally related compounds is then reviewed together with methods available for the quantitative analysis of chlorhexidine. The experimental section describes the evaluation of a HPLC stability indicating method for the quantitative determination of chlorhexidine in terms of sensitivity, precision, reproducibility and selectivity. Comparison is made between this method and the more conventional colorimetric methods based on the Holbrook technique and 4-chloroaniline determination. The degradation kinetics of dilute aqueous solutions of chlorhexidine gluconate have been examined by a pH-stat.ting technique. Over the range pH 2 to 10, 0.002% w/v chlorhexidine gluconate fohowed a pH of maximum stability around pH 5 (at 90°C) with regions uf specific acid/base catalysis presen~. Modifications attributable to a water catalysed reaction (pH 3.5 to 6.5) and presence of unionised chlorhexidine base (pH> 8.5) were also apparent. Concentration dependency was noted at both alkaline and neutral pH. Linear Arrhenius relationships were observed producing -1 apparent activation energies varying from 69.5 to 96.1 kJ.mol •Degradation rate dependence upon ionic strength was consistent with a negative salt effect in alkaline solution. Variable effects on rate were observed in the presence of buffers and with different types of surfactant. Limited studies indicated chlorhexidine solutions are photochemically stable at netural pH but are not amenable to y-irradiation sterilisation. Quantitative analysis of 4-chloroaniline has shown that this compound is not, as previous literature might suggest, the major degradation product of chlorhexidine. HPLC analysis indicates that up to six degradation products may occur. In the discussion an interpretation of kinetic data is presented. Qualitative information from chromatographic studies is used to support a proposed degradation pathway for chlorhexidine. Finally the kinetic data has been used to assess the stability of chlorhexidine to heat sterilisation processes and on long term storage.