An experimental animal model for lymph studies is described. Thoracic duct-venous shunt was established in 12 pigs. Shunt patency averaged 5.5 days. The composition of connective tissue metabolites in lymph and serum were investigated during a standardized surgical operation (thoracotomy) under general anesthesia. We measured the carboxyterminal propeptide of type I procollagen (PICP), the aminoterminal propeptide of type III procollagen (PIIINP) hyaluronan (HA) and total protein. During surgery/anesthesia lymph PICP (p less than 0.04), lymph PIIINP (p less than 0.03) and serum PIIINP (p less than 0.01) and serum PIIINP (p less than 0.03) increased. The changes may be explained by the inactive physical state of the animals. HA showed wide variations, with a tendency like PIIINP. In conscious animals the lymph/serum ratio of PIIINP and HA were 10 and 35, respectively, indicating that lymph is a major route of tissue clearance for these components. The lymph/serum ratio of PICP was 1.0 in conscious pigs, indicating a direct release into the circulation. Total protein in lymph decreased (p less than 0.04) during surgery/anesthesia, whereas no changes were observed in serum. Pigs can be used instead of dogs and sheep in studies on lymph. The effect of surgery/anesthesia must be taken into consideration.