Objectives We assessed the responsiveness of salivary progesterone (P4) and estradiol (E2) to father‐child interaction, including testing for differences in short‐term hormonal change based on paternal characteristics. We also predicted that P4 exposure during the study period would relate positively to post‐interaction paternal mood. Methods We conducted an in‐home intervention study in which fathers (n = 44) played with their toddlers. Subjects provided saliva samples before interacting with their children, with additional collections 40 and 70 min later. Results E2 did not significantly change over the study period (P > 0.4). P4 declined significantly from baseline to 40 min (P < 0.05) and 70 min (P < 0.001). Men reporting that the interaction made them feel very happy/relaxed had greater P4 exposure from baseline through 70 min (area under the curve) compared with men reporting less positive post‐interaction mood (P < 0.05). This relationship persisted after controlling for cortisol. Men's % decrease in P4 (baseline to 40 min) was significantly greater if they had an infant (P < 0.05), while fathers' % decline in E2 (baseline to 70 min) was larger if they had more children (P < 0.05). Conclusions These results require replication but could indicate that grouping fathers with different levels of experience obscures meaningful variation in hormonal responses to child interaction. Our findings appear consistent with the effects of P4 as a mood enhancer and suggest future research should explore the possible role of P4 as hormonal mechanism that could reinforce or facilitate paternal investment. Am. J. Hum. Biol. 25:491–498, 2013. © 2013 Wiley Periodicals, Inc.