By running individual samples of the CF/1-CftrTgH(neoim)Hgu and CF/3-CftrTgH(neoim)Hgu mutant mice together with serial dilutions (5×, 10×, 20×, 50×, 100×) of membranes from the MF1 wild type mice the amount of mature CFTR (band C) in the two inbred mutant mice was estimated to be 9.2 ± 1.5% of wild type for CF/1-CftrTgH(neoim)Hgu and 4.2 ± 2.3% of wild type Cftr protein for CF/3-CftrTgH(neoim)Hgu. The gene discussed is CFTR; the disease is cystic fibrosis.