Withholding iron dextran treatment normally given to pigs at 1-3 days of age to prevent anemia resulted also in neutropenia. Polyinosinic acid:polycytidylic acid (poly I:C) at 0.5 mg/kg IV at 25 days of age resulted in induction of putative interferon 2 to 24 hours later, with significantly (P less than 0.05) lower concentrations in iron-deficient (Fe-) female pigs than in iron-supplemented (Fe+) female pigs. Poly I:C caused several transient toxic manifestations, including elevations in blood urea nitrogen, creatinine, aspartate aminotransferase, potassium (K), total bilirubin and phosphorus (P), marked leukopenia (both neutropenia and lymphopenia), and declines in serum albumin, calcium, cholesterol, glucose and globulin. Certain blood chemistries before poly I:C were significantly (P less than or equal to 0.05) different: albumin, globulin, cholesterol and K were higher in females than in males; albumin, globulin, glucose, P and K were higher in Fe- than in Fe+ pigs; and total carbon dioxide was higher in Fe+ than in Fe- pigs.