Chemical conditioning of sewage was compared in terms of process efficacy, impact upon downstream biological processing and costs for two distinct groups of chemicals. The four chemicals tested were sodium hydroxide, Odomag (a magnesium hydroxide based chemical) [suppression], calcium nitrate and hydrogen peroxide [treatment]. All four chemicals,were able to effectively control odour formation in wastewater. However, the dose sensitivity and stability varied considerably between the options with the magnesium hydroxide providing the most stable system. The impact of each option on the effectiveness of downstream biological treatment was assessed through a closed cell respirometer. Magnesium hydroxide demonstrated a slight overall stimulation of biomass activity at all the doses tested. Whereas all the other options demonstrated either no change or inhibition of biomass activity. A cost comparison of the four options revealed the treatment chemicals were more cost effective for low sulphide concentrations. The critical sulphide concentration varied between 3 and 16 mg 1(-1) depending on the scale of operation and the current market price.