A population composed of 153 plants of "timbó macaquinho" (Derris nicou) 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; e) 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 results indicated that the population was composed of two distinct groups of plants: a) POPULATION A, with 82 plants of low rotenone content (less than 5%); POPULATION B, with 71 plants of high rotenone content (9% or more). In table 16 are presented the minimum, maximum and mean results for both populations. For the plants of population A the fallowing chief mean results were obtained: 1088g of roots; humidity, 6.88%; air dried roots, 1 005 g; ashes, 4.75%; total extracts, 9.84%; rotenone, 2.60%; degueline, 2.85%. For the plants of population B the chief mean results were as follows: roots, 1001g; humidity, 5.31%; air dried roots, 949g; ashes, 5.24%; total extracts, 28.63%; rotenone, 13.53%; degueline, 10.09%. In population A it was observed approximately the following proportion of extracts, in the total extracts: ¹/4 rotenone, ²/4 degueline and ¹/4 other extracts; in population B the proportions were, approximately, as follows: ³/6 rotenone, ²/6 degueline and ¹/6 other extracts. For both populations various correlation coefficients were calculated and were positively and highly significant (P = .01) those between: a) percentage of total extracts and percentage of rotenone; b) percentage of total extracts and percentage of rotenone + degueline; c) percentage of rotenone + degueline and percentage of rotenone.