Identified originally as erythrocyte p80, whose expression is down regulated by the Lutheran inhibitor gene (In[Lu]), the In(Lu) related-p80 glycoprotein represents the red cell isoform of the human cell adhesion/recognition molecule CD44. The presence of a CD44 transcript within a reticulocyte cDNA library was indicated by the PCR amplification of an appropriately sized product generated by a pair of deoxyoligonucleotide primers derived from CD44 cDNA sequence. The amplified product was subsequently utilized to screen and isolate a positively hybridizing full-length reticulocyte cDNA clone (RETIC CD44) that contained an 1809 base pair insert that was DNA sequenced by the dideoxy chain termination method. This first isolate of a reticulocyte CD44 cDNA appears to be generated by a combination of RNA processing events that includes production of 3' mRNA heterogeneity by utilization of multiple poly(A) sites. Remarkably, the 3' untranslated (3'UT) region of this mRNA, encoding a prototypic hematopoietic CD44 isoform, has been previously reported present on only a transcript that encodes a CD44 epithelial isoform.