A population composed of 235 plants of Timbó Urucu (Derris urucu) was studied for selection and establishment of high yielding rotenone clones. The roots were air dried and the humidity content determined. Ashes, total extracts, rotenone + degueline and rotenone were determined by chemical analyses. Individual results of the analyses are presented. From the data were calculated the net weight per plant of: a) air dried roots; b) total extracts; c) rotenone + degueline; d) rotenone; c) degueline; f) other extracts. Were also calculated: g) rotenone content in the total extracts; h) degueline content in the total extracts; i) other extracts in the total extracts; j) rotenone content in the rotenone + degueline complex. The mean weight of dried roots per plant was 1.351kg; for the best 28 plants the dried roots weighed 2.960kg. The ashes averaged 6.28% for 136 plants. The humidity in the air dried roots averaged 5.72%. Part of the data was obtained from determinations made at 100-100°C and part at lower temperature, to avoid rotenone decomposition. This explains the bi-modal curve shown in figure 2. Total extracts averaged 18.32%, varying between 10.2 and 27.2. The average content of total extracts per plant was 246.12g (from a minimum of 3.48 to a maximum of 1234.82g). For the best 28 plants the total extracts averaged 561 grams. Rotenone + degueline averaged 12.67% (from 6.0 to 20.8%). The average rotenone + degueline content per plant was 174.57g (from a minimum of 2.24 to a maximum of 904.37g); for the best 28 plants it was 381 grams. The richest plant had 11.2 % of rotenone an the poorest 2.2%. For the entire population the average content of rotenone was 6.07% and for the best 28 plants it was 7.8%. The average content of rotenone per plant was 84.65g (from 0.88 to 473.62g); for the best 28 plants it was 192 grams. The degueline content of the roots averaged 6.53% (from 1.1 to 11.4%). Other extracts (different from rotenone or degueline) averaged 5.66%. In the total extracts the rotenone content averaged 33.23% (from 13.4 to 53.5%); the degueline content 36.60% (from 9.0 to 69.8%); other extracts 30.32% (from 0.9 to 64.1%). Then, in the population studied the total extracts were composed approximately of 1/3 rotenone, 1/3 degueline and 1/3 other extracts. The "rotenone content of the rotenone + degueline complex varied from 21.4 to 82.5%, averaging 47.94%; then, for the population studied, in this complex the rotenone content was approximately 50%. Various correlation coefficients were calculated and were positively and highly significant (P = .01) those between: a) percentage of total extracts and percentage of rotenone (r = 0.7612; b) percentage of total extracts and percentage of rotenone + + degueline (r = 0.7476); c) percentage of rotenone + degueline and percentage of rotenone (r = 0.8127). Based in the high rotenone content of the roots (from 8.7 to 11.2%) of 12 plants, they were selected for propagation in 1944, when the plants were 19 months old. The roots were collected and the following data obtained: a) The production of green roots averaged 3.951kg per plant; air dried roots averaged 1.717kg per plant; the humidity in the air dried roots (determined at 110ºC) was 11.3%. b) The twelve plants presented an average of 23.6% of total extracts and 10.18% of rotenone. In some cases the results were higher in 1944 than in 1942; in others they were lower. The poorest plant had 6.35% of rotenone and the richest, 15.45%. c) Total extracts averaged 342 grams per plant; rotenone averaged 156 grams per plant. In those 12 plants approximately 45% of the total extracts were represented by rotenone; in the 1942 analyzes of the same plants the rotenone content of the total extracts was 43%.