Sequence analysis of a 5' terminal fragment of stalker retrotransposon, about 1600 bp in length, revealed a number of motifs in the nucleotide sequences of the LTR and other untranslated regions that are common to retrotransposons 412 and MDG1. Taken together, experimental data and computer analysis of this sequence suggest that stalker falls into the gypsy group of retrotransposons and most closely resembles related retrotransposons 412 and MDG1. Stalker bears a small open reading frame (sORF) that shares 24 and 75% identical amino acid residues with the second sORFs of retrotransposons 412 and MDG1, respectively. Thus high similarity between the discovered sORF of stalker and the corresponding frame of MDG1 looks intriguing, since other regions of the sequences display little resemblance. Therefore, the evolutionary proximity of stalker to MDG1 cannot be conjectured solely on the basis of the mentioned similarity. The similarity may be explained by recombination of the two transposons, or, alternatively, the frame can retain its function in the genomes of stalker and MDG1 and lose it in 412.