Long interspersed elements (LINEs, L1s) are non-long terminal repeat (LTR) retrotransposons found in mammalian genomes and account up to 20% of genomic DNA. It has been shown that active L1 elements can cause mutation resulting in disease, genetic variation and polymorphisms and their inactive copies seem to be involved in recombination and rearrangement. L1–encoded products have been detected in a number of tissues including mammalian germ cell tumours, breast carcinomas and a large variety of transformed mouse and human cell lines. Chinese Hamster Ovary (CHO) cells are widely used in the manufacture of recombinant proteins for biopharmaceuticals. Here, we investigated the transcriptional activity of hamster L1 elements in CHO-K1 cells. These cells were analysed for the presence of L1 RNA transcripts. The sequence, which is homologous to mammalian L1 elements, was cloned from hamster genomic DNA and used to design primers for RT-PCR. L1 transcripts were detected in CHO-K1 RNA.