This paper describes two unusual cases where fungal infections of the toenails caused dark pigmentation (melanonychia). The first patient had a combination of two fungi (Aspergillus hiratsukae and Trichosporon faecale) causing black nail streaks, while the second had Exophiala xenobiotica and Trichophyton interdigitale causing dark-brown discoloration. Both patients were successfully treated with an antifungal medication called efinaconazole over several months.