Two experiments to study the development of the meaning of laughter in children are reported. A pilot study presented recorded audio tapes with both humorous and nonhumorous episodes, some with accompanying canned laughter, to 24 boys between the ages of 4 and 6 years. Observers recorded durations of laughter and smiling. Results showed that both responses reflect social context, and occur more in a group situation. Four-year-olds smiled more when alone than 6-year-olds who smiled most when in the group situation. The two groups gave different responses in rating stimuli as humorous. Humor responses and ratings were not correlated. In the second study, 48 4- and 6-year-old boys, in groups of three, listened to two audio tapes which contained essentially nonverbal humorous and nonhumorous stimuli. On one tape the third stimulus was followed by 10 seconds of silence, on the second tape by 5 seconds of laughter and 5 of silence. Videotapes showed that 6-year-olds laughed and smiled with the laugh track more than 4-year-olds. Laughter and smiling were significantly related at age 4 but not at age 6. This study supports the hypothesis that the social mirth response, in terms of both live group and recorded laughter, is developmental in nature. (DR)