Perception and production data were collected from 28 children, ages 1; 8 to 3; 11, to test four specific hypotheses on the acquisition of initial fricatives and glides in English, based on the assumptions that perception precedes production and unmarked precedes marked. Perception data were collected by the Shvachkin-Garnica technique for ‘phonemic perception’. Pairs of objects are given nonsense names, CVCs differing only in the initial sound; the child is asked to perform certain actions with the named objects and if he is correct on 7 out of 10 trials he is assumed to have demonstrated phonemic perception of the opposition in question. Production data were compared to the perception data. Results only partially confirm the hypotheses and indicate that (a) children as late as age 3; 0 do not have complete phonemic perception, (b) phonemic perception develops gradually, generally in advance of production, and (c) the order of acquisition shows trends toward uniformity but is not universal.