This report concerns the ability of fish-populations in the Neosho and Marais des Cygnes rivers in Kansas to readjust to continuous stream-flow following intermittent conditions resulting from the severest drought in the history of the State. The variable weather in Kansas (and in other areas of the Great Plains) markedly affects its flora and fauna. Weaver and Albertson (1936) reported as much as 91 per cent loss in the basal prairie vegetative cover in Kansas near the close of the drought of the 1930's. The average annual cost (in 1951 prices) of floods in Kansas from 1926 to 1953 was $35,000,000. In the same period the average annual loss from the droughts of the 1930's and 1950's was $75,000,000 (in 1951 prices), excluding losses from wind- and soil-erosion. Thus, over a period of 28 years, the average annual flood-losses were less than one-half the average annual drought-losses (Foley, Smrha, and Metzler, 1955:9; Anonymous, 1958:15). Weather conditions in Kansas from 1951 to 1957 were especially noteworthy: 1951 produced a bumper crop of climatological events significant to the economy of the State. Notable among these were: Wettest year since beginning of the state-wide weather records in 1887; highest river stages since settlement of the State on the Kansas River and on most of its tributaries, as well as on the Marais des Cygnes and on the Neosho and Cottonwood. The upper Arkansas and a number of smaller streams in western Kansas also experienced unprecedented flooding (Garrett, 1951:147). This period of damaging floods was immediately followed by the driest five-year period on record, culminating in the driest year in 1956 (Garrett, 1958:56). Water shortage became serious for many communities. The Neosho River usually furnishes adequate quantities of water for present demands, but in some years of drought all flow ceases for several consecutive months. In 1956-'57, the city of Chanute, on an emergency basis, recirculated treated sewage for potable supply (Metzler _et al._, 1958). The water shortage in many communities along the Neosho River became so serious that a joint project to pump water from the Smoky Hill River into the upper Neosho was considered, and preliminary investigations were made. If the drought had continued through 1957, this program might have been vigorously promoted. Data on stream-flow in the Neosho and Marais des Cygnes (1951-'59) are presented in Tables 1-4. These severe conditions provided a unique opportunity to gain insight into the ability of several species of fish to adjust to marked changes in their environment. For this reason, and because of a paucity of information concerning stream-fish populations in Kansas, the study here reported on was undertaken. TABLE 1. STREAM-FLOW IN CUBIC FEET PER SECOND, NEOSHO RIVER NEAR COUNCIL GROVE, KANSAS. DRAINAGE AREA: 250 SQUARE MILES.