Abstract: The present disclosure is concerned with a technique for producing storage stable, non-caking, low viscosity pesticidal concentrates and the compositions so obtained. The technique involves milling a solid biologically active compound in a low viscosity aliphatic petroleum fraction in which it is slightly soluble until it has an average particle size of less than about 10 microns at a temperature in excess of about 40.degree. C. in the presence of a high or ultra-high surface area silica and lecithin. The milling is conducted in such a manner as to avoid melting any significant portion of the biologically active compound undergoing milling. The concentrate so obtained, typically display room temperature viscosities between about 20 and 2,000 cps and contain between about 120 and 480 grams per liter of biologically active compound.