The test of gel-electrophoresis applied to the pox virus group showed to be at least thirth times (30X) more sensitive than agar-gel test on the described conditions (Table I). Twelve specimens, which were positives form Smallpox in the conventional tests of egg inoculation and agar-gel difusion test, have been screened in their original dilutions frozen for more than 1 year and six of them were still detectable by gel-eletrophoresis, while by agar-gel test any of them was positive (Table II). Thirty three Smallpox isolates have been tested with material from first egg inoculation (chorioallantoic membranes) which have been stored in glycerin 50%, at - 15ºC. Fifteen of them were still positive by gel-electrophoresis and only 3 by agar-gel (Table II). The last 60 specimens received for diagnosis from Smallpox Erradication Campaign (CEV), were negatives by both tests. The gel-electrophoresis, did not show false-positives on described conditions.