Effect of genetic background on CF mouse survival on solid chow. Mice were maintained on the liquid diet (Peptamen) until 8 weeks of age, at which time they were fed standard solid mouse chow for up to 8 additional weeks. Deaths were recorded as they occurred and mice in obvious distress were sacrificed and 'death' recorded as the subsequent day. By log-rank test, CF mice on the mixed background had significantly earlier death compared to wild type (P = 0.035), and significantly later death than CF mice on the B6 background (P = 0.025). CF mice on the B6 background also died significantly earlier than wild type (P < 0.0005).