SummaryThis study utilized isoelectric focusing and electrophoresis in an attempt to detect a cystic fibrosis (CF) scrum factor(s), for which there is considerable indirect evidence. The method of isoelectric focusing in polyacrylamide gels (IEFAG) specified by Wilsonet al.(53), as reproduced in our laboratory, did not enable the detection of a CF factor protein reported to focus near pH 8.4–8.5. Consequently, we employed our modified IEFAG techniques, which enabled us to demonstrate significantly enhanced resolution and striking heterogeneity in serum γ-globulins. Despite the significant increase in the number of bands resolved by our methods, neither a difference at pH 8.4–8.5 nor other differences throughout the alkaline pH range could be detected consistently in the CF and heterozygous sera. The two-step IEFAG/disc electrophoresis technique outlined by Alt-landet al.(2), as reproduced in our laboratory, indicated that at least one small, cationic protein could be fractionated from all serum samples. Improvements in the method of disc electrophoresis resulted in the observation of numerous bands from some samples and of differences among the samples, but no protein band unique to the CF genotypes was observed.Our approach, employing different electrophoretic techniques and varying the conditions of sample analysis, should have increased the likelihood of detecting a protein or proteins specific for the CF genotypes. Despite the many variations in our approach, no consistently unique protein was observed in the CF or heterozygous sera.SpeculationA CF serum factor cannot be readily demonstrated by the electrophoretic techniques described. The value of the “biophysical assay” and the “nonbiologic technique” reported in the literature is suspect, and the promise and applicability of these techniques as diagnostic tests for the CF gene should be carefully evaluated.