Disclosed is solid fipronil (formula I) comprising at least 98% by weight of the crystalline modification V fipronil showing, in an X-ray powder diffractogram recorded using Cu-Ka radiation at 25 degrees C, at least 3 of the following reflexes: (1) 2theta = 10.3 ± 0.2 degrees (2) 2theta = 11.1 ± 0.2 degrees (3) 2theta = 13.0 ± 0.2 degrees (4) 2theta = 16.2 ± 0.2 degrees (5) 2theta = 20.3 ± 0.2 degrees (6) 2theta = 31.5 ± 0.2 degrees and a melting point in the range of 201 to 203 degrees C. Also disclosed is a process for preparing crystalline modification V fipronil comprising the steps of: step i) preparing a solution of a solid form of fipronil being different from the crystalline modification V in a solvent S selected from dimethylsulfoxide having a temperature of 100 degrees C to 150 degrees C or acetonitrile having a temperature of 60 degrees C to 81degrees C step ii) effecting crystallization of fipronil from the solution and step iii) isolating the resulting precipitate. Also disclosed is the use of the crystalline modification V fipronil for the control of pests and methods of control of pests such as parasites, insects, arachnids or plant nematodes.
