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The life history of the teardrop darter, Etheoctoma (Catonotus) barbouri Kuehne and Small, was intensively studied from September, 1972, through August 1973. A total of 299 teardrop darters was seined from two isolated populations in Alexander and Little Muddy Creeks, Kentucky. These darters are known only to occur in second, third or fourth order tributaries of the Green River in Kentucky and Tennessee, and normally seek protection afforded by rocky or vegetated edges of such streams. Gonosomatic ratios indicated that teardrop darters spawned from late March through late May in waters 12.5 - 15.5 C. Young females developed primary ova at a later date than did their older counterparts. Fry were first collected in late May in shallow riffles. Longer fish produced a greater number of mature eggs than did the shorter fish. Males were the predominant older fish; apparently few females survived to their second birthday. Length-frequency distributions and scale annuli readings inidcated three age groups - 0, I and II. Average standard lengths at these stages were 30, 41 and 46 mm. Darters gained the greatest percentage of weight during the second year of life. The faster-growing fish of Little Muddy Creek were shorter-lived than the slower-growing fish of Alexander Creek. The length-weight regression values of all fish, except female and non-sexed fish from Little Muddy Creek, were greater than 3.0. Coefficients of condition, lowest in the fall and highest in the spring months, indicated that slower-growing fish were slightly more plump than were faster-growing fish. Teardrop darters were carnivorous througout life. The most numerous food items ingested were cladocerans, chironomids, copepods and simullius. Chrironomid midge larvae were the most frequent food items ingested. Cannibalism did occur. Spring and winter months were periods of heaviest feeding. Alexander Creek darters were characterized by narrower ranges in number of fin spines and soft-rays, total and pored lateral line scales, and cephalic canal pores. One-half of the darters collected had "black-spot", Neascus of Crassiphiala bulboglossa, while about seven percent had internal mesentery nematodes (Contracaecum sp.), but harmful effects were not noted on the darters. Possible fish predators included the banded sculpin, grass pickerel and large creek chubs. Water snakes, snapping turtles, belted kingfishers and green herons may also have preyed on teardrop darters. Etheostoma barbouri occupied an ecological position most closely related to that of its darter associates. In conveniently shared the stream substrate with other darter species which were found most often in the deeper rocky portions of pools.