Equations for estimating the 7-day 2-year and 7-day 10-year low flow at sites on ungaged streams are presented. Regression analysis was used to develop equations relating basin characteristics and low-flow characteristics at 58 continuous-record gaging stations and 151 partial-record sites. Significant basin characteristics in the equations are drainage area and percentage of drainage basin underlain by permeable bedrock units. The study area, which encompasses the western two-thirds of the State, is divided into three regions based on the similarity of basin characteristics within each region. The analysis includes records for only those stations that are not highly regulated and have drainage areas less than 1,000 square miles.A three-step method is used to estimate low-flow characteristics at ungaged sites. The first step involves the use of a logistic regression to determine the probability that the 7-day annual minimum flow is zero at the site of interest. The second step uses this estimated probability of 7-day annual zero flow to determine if the estimated value of the 7day 2-year or the 7-day 10-year low flow is zero or needs to be estimated from one of the regional equations, which are based on a generalized-least-squares model for sites with non-zero flow. The third step involves the use of the regional equation, if flow is indicated, to determine the 7-day 2-year and 10-year low-flow values.Computer software has been written to facilitate the computation of low-flow characteristics at sites of interest The software is provided in written form and on a disk. «(*) «(*) =-^-rŵ here *W = P