New phthalocyanin derivatives which can be used to differentiate basophils from other blood cells are disclosed. The compounds to which the present invention are quaternary salts of a substituted phthalocyanin structure wherein the substitutions are each independently hydrogen, sulfonate, or a C.sub.1 -C.sub.7 hydrocarbon, optionally containing at least one heteroatom, with the proviso that at least one of them is ##STR1## in which R.sub.1 -R.sub.3 are each independently lower alkyls, cycloalkyls or olefins of which at least one is C.sub.2 -C.sub.4 and two may join to form a ring; R.sub.4 is hydrogen or a C.sub.1 -C.sub.3 alkyl; n is an integer from 1 to 6; M is a polyvalent metal ion. It is preferred that at least two and especially at least three substitutions have the structure so set forth.