Fiber-reactive, heavy metal-containing formazane dyestuffs are disclosed which are tricyclic and wherein the heavy metal is a metal of an atomic number ranging from 24 to 30 and is bonded via a --COO-- and --O-- substituent to different diazo components and to the terminal nitrogen atoms of the central formazane bridge portion ##STR1## wherein R represents an optionally substituted aliphatic hydrocarbon radical, a cycloaliphatic radical or a carbo- or heterocyclic-aromatic radical, one of the aforesaid diazo components or the radical R bearing the fiber-reactive substituent. These dyestuffs are useful for the dyeing and printing of textile materials, and also of synthetic materials for other then textile uses. The dyestuffs may contain or may be free from watersolubilizing groups the former being especially useful for the dyeing of leather, paper, and natural or synthetic polypeptide fiber materials, as well as for the dyeing and printing of material or regenerated cellulosic fiber materials, especially cotton. Dyestuffs in which this fiber-reactive substituent is a pyrimidyl amino radical containing at least one fluorine atom are distinguished by their high reactivity; dyeings or prints obtained therewith are very stable vis-a-vis acid or alkaline hydrolysis and exhibit very good fastness to light, milling and wet treatments.