The segments in long germ-band insect embryos, like Drosophila, are all determined at syncytial blastoderm stage. This is in contrast to short germ-band embryos which show an early determination of only the anterior head segments, whereas the more posterior thoracic and abdominal segments are sequentially added after formation of a primary germ anlage (reviewed in ref. 1). Segment formation in Drosophila involves the pair-rule genes which define double segmental periodicities and which have been considered to represent a special adaptation to the long germ-band type development hairy belongs to the primary pair-rule genes in Drosophila which are directly regulated by the gap genes, such as Krüppel. We have isolated the orthologues of hairy and Krüppel from the flour beetle Tribolium castaneum which has a short germ type development. We show here that hairy is expressed in several stripes at blastoderm stage and later on in two stripes in the growth zone of the developing embryo. Krüppel expression overlaps hairy stripe three and four expression, very similar to Drosophila. This suggests that the segment patterning mechanism that acts in an open blastoderm in Drosophila works in a similar way in the cellularized Tribolium embryo.