The production of brook trout (<i>Salvelinus fontinalis</i>) in four headwater streams was studied with respect to natural variation in production and turnover ratios, contribution by age group and time of year, and correlations of physical and chemical variables with production. Lick Run and Ewings Run are spring fed streams with relatively high conductivity (105-135 µmhos). Guys Run and the South Fork of Potts Creek (SFPC) have moderate (25-63 µmhos} and low (17 µmhos) water conductivity, respectively. Two 200 m sections, each divided into four 50 m replicates, were studied in each stream. Annual production of brook trout averaged 45.4, 13.9, 17.2 and 14.0 kg ha^-1yr^-1 for Ewings Run, Lick Run, Guys Run, and SFPC, respectively. Production estimates were more variable within streams than among streams. Turnover ratios were consistent among streams and averaged 3.0 (s.d.=1.0} for age 0 trout, 1.3 (s.d.=0.4) for age 1 trout, and 1.6 {s.d.=0.4) for all ages combined. Age 1 trout contributed an average of 39% to annual production estimates. Age 0, 2, and 3 fish averaged 30%, 24%, and 7% of annual production estimates. Over 90% of the annual production of brook trout occurred between December and July. The December to May and May to July periods had equal levels of production of adult trout. The May to July period had the highest production of age 0 trout. The July to October period had the lowest production for all ages and the greatest incidence of negative production. No meaningful correlations of production with percent pool, percent bedrock, conductivity, discharge, or surface area were found. It was concluded that variables relating to habitat quality, such as instream cover, may have a more detectable effect on production than broad environmental variables. / M. S.