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Most protozoan parasites, such as Leishmania, Plasmodium, Toxoplasma and Trypanosoma, rely on a salvage pathway for their supply of purine ribonucleotides (Wang, 1984). Inhibition of this pathway therefore presents an interesting approach in the fight against microbial infections. To explore the feasibility of this approach we have attempted to identify inhibitors of the essential purine salvage enzyme hypoxanthine-guanine-xanthine phosphoribosyl transferase (HGXPRTase) of the protozoan parasite Tritrichomonas foetus. This sexually transmitted parasite causes causes bovine trichomoniasis, which can lead to embryonic death and infertility in cows. T. foetus relies primarily on a single enzyme, HGXPRTase, to transfer ribose 5-phosphate from α-D-5-phosphoribosyl-1-pyrophosphate to the N9 nitrogen atom of hypoxanthine, guanine or xanthine (Wang et al., 1983). Selectivity with respect to the mammalian enzyme hypoxanthine-guanine-phosphoribosyl transferase (HGPRTase), that has 27% sequence identity with the parasite enzyme, is important to avoid serious side effects. Currently available inhibitors are purine analogues with affinities in the millimolar range (Jadhav et al., 1979). Here we report the use of the molecular docking program DOCK 3.5 (Kuntz et al., 1982; Meng et al., 1993) for the discovery of more potent, novel inhibitors of HGXPRTase that are selective with respect to the human enzyme (Somoza et al., 1998).