Individually tested 5 lactating female, 10 primed and 10 naive female and male TO Swiss mice for approach responses to an electronically generated model of a newborn mouse pulse in a small choice chamber. Lactating females and primed females made more responses than did other mice, and priming increased the responsiveness of both males and females. In the 2nd experiment with 42 naive female Swiss mice, primed females were tested with 5 different electronically generated ultrasonic signals. More approaches were shown to a 65-45 kHz signal than to one of higher or lower frequency but of the same bandwidth. An 80-msec pulse elicited more approach responses than a 15-msec one. In a 3rd experiment the responses of 14 primed female house mice showed a slightly lower response level but, like TO Swiss mice, made more approaches to a pulse of 65-45 kHz than to one of 75-55 kHz. It is suggested that the use of electronically generated signals may help reveal important features of infant rodent calls that elicit adult approach behavior. The method allows greater flexibility than does the use of replayed tape recordings.(1 p ref)(PsycINFO Database Record (c) 2016 APA, all rights reserved)