Apolipoprotein AIV is one of the principal apolipoproteins synthesized by the rat small intestine. We have cloned a cDNA encoding a portion of preapolipoprotein AIV mRNA. A kinetically fractionated cDNA probe highly enriched for the abundant intestinal mucosal mRNA sequences was used to screen a library of recombinants containing cDNA generated from total intestinal epithelial mRNA. The abundant class of mRNA sequences was defined by hybridization analyses. This frequency class had an aggregate complexity of 5300 nucleotides and represented 25% of accumulated mRNA sequences.l The mRNAs comprising this class were identified by in vitro translation and included preapolipoprotein AIV, preproapolipoprotein AI, intestinal fatty acid binding protein, and liver fatty acid binding protein. A cDNA-containing clone derived from preapolipoprotein AIV mRNA was identified among probe-positive recombinants. This cDNA was used to establish that apolipoprotein AIV mRNA has a mass of 550000 daltons (equivalent to 1780 nucleotides) and represents 0.013% of total cellular RNA in the fasting state. Acute feeding with triglyceride-rich meals resulted in a 2-fold increase in preapolipoprotein AiV mRNA after 4 h.