Abstract: Disclosed herein are a novel compound, 5-methylthiopyrimidine derivative, notably that represented by the following general formula: ##STR1## wherein X means an oxygen or sulfur atom and R.sup.2 denotes a methyl, allyl or propargyl group, its preparation process and an agricultural and horticultural fungicide containing same as an active ingredient. The above compound exhibits outstanding control effects against plant diseases, especially, late blight of potatoes and the like and downly mildew. It permits preparation of an ideal agricultural and horticultural fungicide owing to its very low toxicity against mammal and fish and its no phytotoxicity.

Abstract: Novel compounds of the formula: ##STR1## wherein R.sup.1 is lower alkyl; R.sup.2 is hydrogen or lower alkyl, which are produced by reacting a compound of the formula: ##STR2## wherein R.sup.3 is hydrocarbon residue, with a compound of the formula: ##STR3## The novel compounds have antiviral and antibacterial activity, and are useful to prolong the life span of tumor-bearing warm-blooded animals.