In an effort to etablish new candidates with improved antineoplastic, anti-HIV-1 and antimicrobial activities, the synthesis of some new triazino and triazolo[4,3-e]purine derivatives is described: 6,8-dimethyl-1, 4-dihydro-1,2,4-triazino[4,3-e]purine-7,9(6H, 8H)-diones 3–6; 5,7,9-trimethyl-1,2,4-triazolo[4,3-e]purine-6,8(5H, 7H, 9H)-diones 11–13, together with the synthesis of the 8-substituted purine derivative: 8-(3,5-diamino-1H-pyrazol-4-yl)diazenyl-1,3-dimethyl-1H-purine-2,6(3H, 7H)-dione 7. The prepared compounds were tested for their in vitro anticancer, anti-HIV and antimicrobial activities. The results of the in vitro anticancer screening revealed that compound 3 exhibited considerable activity against melanoma MALME-3 M, non-small lung cancer HOP-92 and breast cancer T-47D (GI50 values of 25.2, 31.8, and 32.9 lM, respectively). The anti-HIV-1 results indicated that compounds 7 and 13c displayed moderate activity (maximum % cell protection 30.52 and 35.54 at 2 9 10-4 M, respectively). The in vitro antimicrobial data showed that compound 12 was the most active against P. aeruginosa, it was equipotent to ampicillin (MIC\100 lg/ml). While compound 11d was the most active against P. vulgaris, it was as active as ampicillin (MIC\50 lg/ml). In addition, compounds 12 and 13c were the most active against S. aureus (MIC\50 and\25 lg/ml, respectively). On the other hand, the tested compounds devoid of antifungal activity except 6b and 11c which showed weak activity against A. niger.