To promote understanding of the authority of the primary literature in students taking our biochemistry laboratory courses, a biochemistry laboratory exercise on the determination of an acceptable molar absorptivity value of 2-nitrophenol (2-NP) was developed. This made the laboratory course much more relevant by linking to a thematic thread, [beta]-galactosidase, that scaffolds concepts in one exercise with those in later exercises. The substrate for the continuous assay of [beta]-galactosidase is the chromogenic 2-nitrophenyl-[beta]-D-galactopyranoside that produces 2-NP. In an early laboratory exercise, students determine the wavelength of maximum absorption for the protonated and deprotonated form of 2-NP at various pH values and then determine the molar absorptivity of 2-NP. Students were encouraged to discuss apparent discrepancies not only in their own determinations of molar absorptivity values for 2-NP, but also in the published molar absorptivity values for 2-NP (2,150-21,300 M[superscript -1] cm[superscript -1]) at almost the same pH and at 420 nm. Finally, the students were led to a publication that serves as an authentic source for molar absorptivity of 2-NP. (Contains 3 figures, 2 tables, and 1 footnote.)