In bovine conceptuses, the trophoblast elongates rapidly from the 13th to the 19th day of pregnancy, while the embryonic disc differentiates to set up the primary germ layers and the axis of the fetus. Observations on pregnancies of cloned fetuses underline placental abnormalities which could originate from earlier gene deregulations occurring during this long pre-implantation period. To allow screenings with individual trophoblasts we used amplification protocols involving either PCR or in vitro transcription steps. For that purpose we used a bovine-specific macro-array starting from a cDNA library generated on early in vivo elongating conceptuses. RNAs from adult somatic tissues were used to compare hybridisation patterns generated with amplified and unamplified polyA+ probes.