The author's experimental data on cDNA libraries for different rat tis
sues and cultured murine embryo stem cells are used to offer a number
of methodical improvements that enhance the efficiency of cloning in l
ambda ZAPII/pBluescript. The modifications are of general nature and m
ay prove helpful with other vectors, in constructing both common cDNA
libraries and specifically enriched ones to search for differentially
expressed genes.