Results of RT-PCR using primers 4 and 3 (see Fig. 1A) with: (A) 6 independent samples of secretory phase endometrial tissue cDNA. Lanes 1 and 2 are early, 3 and 4 mid, and 5 and 6 late secretory phase samples. Different patterns of product relative abundance were not found in particular phases. (B) RT-PCR using endometrial carcinoma cell lines HEC1A (1), HEC1B (2), AN3-CA (3) and the breast carcinoma cell line T47D (4). Controls in which cDNA was omitted were always negative (B, lane 5). The 686 bp product is predicted to encode a secretory isoform of MUC1.