Abstract The contributions of the glucose catabolic pathways in different stages of the life cycle of the cattle tick, Boophilus microplus , were estimated on the basis of rates of 14 CO 2 production from specifically labelled glucose. In free-living larvae the pentose cycle accounted for 20 per cent of the total glucose catabolism. In female ticks in the final 24 hr of parasitic feeding and in the pre-oviposition period the pentose cycle proportion rose to over 50 per cent and returned in the final stage of oviposition to 20 per cent. These changes are attributed to the importance of the pentose cycle in biosynthetic processes which must reach their peak during vitellogenesis in the pre-oviposition period.