[en] In January 1994, a pipeline in the Rocky Mountain foothill region of Alberta leaked sour gas and condensate, including volatile hydrocarbons, into the Red Deer River. Cattle on two ranches were within 4 km to less than 0.5 km from the leak site. Once the leak was discovered (about three days after the rupture) the well was shut in and the pipeline was purged of crude petroleum. The cows at both ranches were brought into confined areas for clinical observations. Calving started in mid-January at both ranches. Many of the calves and cows exhibited abnormal behaviour. An investigation into the possible toxicological effects of the leak emissions in cattle was conducted in order to assess the health and productivity of the cattle on the two ranches and to evaluate plausible etiologies for observed adverse effects in the cattle. Another objective was to obtain exposure analyses. Both ranches had a higher mortality in 1994 compared to previous years. Results showed evidence, by way of clinical signs and histopathologic lesions in the respiratory, nervous, and lymphoid tissues, of exposure to volatile hydrocarbons released at the time of the leak and during the subsequent cleanup operations. However, there were also other factors (BVD virus and Salmonella and corona virus infections, neonatal diarrhea, selenium and copper poisoning), that have contributed, although no consistent pattern of disease other than immune dysfunction could explain the high death losses observed among calves on the two ranches. 63 refs., 20 tabs., 12 figs., 5 appendices