Abstract: A miniature fuse comprises a casing mounted on a base member and having a meltable fuse-link housed within the casing above the upper surface of the base member. The casing has a transparent portion and a substance of contrasting color with respect to the upper surface of the base member is interposed between the casing transparent portion and the base member upper surface. The substance is heat-sensitive to temperatures at and above those at which the fuse-link melts and undergoes a reaction in which the substance is consumed by the heat generated during melting of the fuse-link. The state of the fuse can be readily determined by viewing the transparent portion of the casing and when the fuse is in its non-blown state, the color of the substance is visible through the transparent portion whereas when the fuse blows, the substance is consumed and the contrastingly colored upper surface of the base member becomes visible through the transparent portion thereby indicating the blown state of the fuse.