Pyrimidine is found as a core structure in a large variety of compounds that exhibit important biological activity, specifically pyrimidines known to inhibit Pneumocystis carinii (pc), Toxoplasma gondii (tg) of tumour cell lines in culture and the activity is attributed to inhibition of dihydrofolate reductase (DHFR) [11]. The gene discussed is DHFR; the disease is neoplasm.