The boxing film project was shelved and Vasile offered Castellari to direct Day of the Cobra.

[2] Castellari cast many actors who he had previously worked with, including Franco Nero and Massimo Vanni.

[2] Day of the Cobra was shot on location in San Francisco, Genoa and at Incir-de Paolis in Rome.

[1] According to the German book Der Terror führt Regie: "Day of the Cobra is technically pure cinema.

The rooftop chase that opens the film is quite exciting and there is also a memorably tongue-in-cheek scene where Nero dukes it out with a transvestite in an empty disco.