A retrospective survey to determine the effect of space allowance on in-transit losses of  finisher pigs in summer temperatures in June, July and August 2003. Both 2- and 3-tiered  trailers were considered that transported greater than 130 pigs to 3 main Ontario packing plants processing 76% of all Ontario market hogs. Packer data was combined with daily in-transit loss data to determine the number of pigs that were transported on that trailer and space allowance was determined from the trailer’s capacity and the number of pigs transported. Environmental temperature and relative humidity data was provided by 2 local Ontario weather stations and were considered on a hourly basis. As environmental temperature increased, in-transit losses  increased. As space allowance decreased, in-transit losses increased when the temperature was  constantly below 21°C however by a lesser amount than was seen with temperature. Overall, it was found that temperature had a greater affect on piglet in-transit losses than space allowance   however increasing space allowance allows pigs to cool more efficiently and will therefore  decrease pig in-transit losses.