There are provided, as novel herbicides, the substituted pyrazolopyrimidines of the formula: ##STR1## where A represents -CO-NR.sup.6 - or -C(OR.sup.7).dbd.N-, and R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.6 and R.sup.7 are substituent groups as defined in the specification, and the salts and acid addition salts thereof. Processes for their preparation are provided, as also are herbicidal compositions containing them and methods of combating weeds in which they are used.