Abstract: Pyrazolo?1,5-a!pyrimidine derivatives of the formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are H, carboxyl, lower alkoxy-carbonyl, phenyl, lower alkyl optionally having a substituent selected from OH, carboxyl and lower alkoxy-carbonyl, or cycloalkyl, or R.sub.1 and R.sub.2 may combine each other to form lower alkylene; R.sub.5 is group of --SR.sub.6 or group of --NR.sub.7 R.sub.8 in which R.sub.6 is pyridyl or phenyl optionally having 1 to 3 substituents selected from OH and lower alkyl; and R.sub.7 and R.sub.8 are H, phenyl optionally having 1 to 3 substituents selected from OH, lower alkyl, lower alkoxycarbonyl and carboxyl, or R.sub.7 and R.sub.