We experimentally investigated the influence of amplified spontaneous emission within the Brillouin gain bandwidth on the Brillouin scattering of a single-frequency signal. The experiments were performed for the case of artificial ASE injected in backward direction into a passive fiber, as well as in forward direction of a low-power fiber amplifier. A significant influence could be observed, when the ASE was counter-propagating to the signal. Injecting 160.6nW of ASE within the Brillouin gain bandwidth led to a decrease of about 3 dB of the SBS-threshold of an approximately 335m long passive fiber from about 80mW to less than 40mW. At a fixed signal power of 81 mW the backscattered power and the power in the Brillouin scattered Stokes maximum increased by a factor of 19.