The results of the present study demonstrate a well-developed olfactory sensitivity of spider monkeys for aliphatic ketones.All animals significantly discriminated dilutions as low as 1:100 with 2-butanone, 1:1 000 with 2-pentanone, 1:3 000 with 2-hexanone, 1:10 000 with 2-heptanone, 1:10 000 with 2-octanone, 1:3 000 with 2-nonanone, 1:30 000 with 3-heptanone and 1:30 000 with 4-heptanone from the solvent. Some of the animals detected even lower dilutions of these odorants. With four of the odorants the threshold values between the most- and the least-sensitive animal differed only by a dilution factor of 3 (2-pentanone, 2-butanone, 3-heptanone and 4-heptanone). With two of the odorants the animals’ individual threshold values differed by a dilution factor of 10 (2-nonanone and 2-octanone). The animals’ sensitivity differed by a factor of 33 for 2-hexanone and 300 for 2-heptanone.

The majority of dilutions at threshold correspond to gas phase concentration values lower than 1 ppm (parts per million). However, for three of the odorants (2-hexanone, 2-pentanone and 2-butanone) the values of ppm are higher than 1 with the highest value reaching as high as 1037 (for 2-butanone). 

There is a significant negative correlation between the threshold values and the numbers of carbons. The linear regression analysis reveals that for each carbon on the chain the olfactory sensitivity increases with -0.622.
 There was no significant correlation between the positioning of the keto-group and the threshold values for the three different heptanone molecules (2-heptanone to 4-heptanone).