Following outbreaks of bovine spongiform encephalopathy (BSE), fewer cattle mortalities are being rendered. Additionally, meat processors are facing increased costs for disposal of specified risk materials (SRM). SRMs have a higher risk of carrying and transmitting infective BSE prions. Composting may be a viable alternative for disposal of cattle carcasses and could form part of a disposal plan for SRM. A study was conducted to assess feasibility and greenhouse gas (GHG) emissions during co-composting of cattle mortalities and SRM with cattle manure. Compost windrows were constructed and contained manure + straw + cattle mortalities (treatment; CM) or manure + straw + SRM (SRMM) and replicated four times. Based on the availability of cattle mortalities, SRM and manpower, the CM and SRMM composting windrows were constructed over a span of 50 days (March 30 to May 18, 2006). The composting periods were shorter for SRMM (133 to 147 days) than for CM (190 to 217 days). The average surface GHG flux for the CM treatment were 21.93 mg C min^-1m^-2, 1.090 mg C min^-1m^-2 and 0.117 mg N min^-1m^-2, for CO₂, CH₄ and N₂O, respectively, and were not significantly different from those of SRMM (16.87 mg C min^-1m^-2, 0.486 mg C min^-1m^-2 and 0.120 mg N min^-1m^-2 for CO₂, CH₄ and N₂O respectively). However, the cumulative surface GHG emissions of 6.49 kg C m^-2 (CO₂), 0.321 kg C m^-2 (CH₄) and 0.034 kg N m^-2 (N₂O) were significantly higher in CM due to a longer composting period than the values of 3.32 kg C m^-2(CO₂), 0.096 kg C m^-2 (CH₄) and 0.024 kg N m^-2 (N₂O) for SRMM. All SRM and most cattle mortalities (except a few large bones) were decomposed so composting may be a viable option for their disposal.