Frequency discriminability of pure tones was measured in a variety of background noise conditions. Difference limens were estimated at 4 kHz using a method of constant stimulus differences, Maskers included wide‐band white noise, low‐pass noise at 1 kHz, high‐pass noise at 6 kHz, and a 500‐kHz tone. In all cases the test signal was held at 15 dB SLrequite or masked threshold. Initially measures were obtained with 20 dB of masking for each condition, Frequency DL's in wide‐band and in high‐pass noise were comparable to those in quite. In low‐pass noise and in the low‐frequency tonal masker, DL's were significantly greater than in quiet. When the amount of masking was changed (SL of signal held constant). DL wide‐band noise was approximately constant while DL in low‐pass noise increased with noise level. These results are discussed in relation to single nerve‐fiber tuning curves in noise and also in relation to data on two‐tone suppression effects.