This paper presents an analysis of abscission reponses of cotton explants to (a) 1-naphthaneneacetic acid; (b) photodecomposition products of 1-naphthaleneacetic acid: 1-methylnaphthalene, 1-naphthaldehyde, 1-naphthoic acid, naphthalene, and phthalic acid; and (c) a related compound: naphthaleneacetyl aspartate. Abscission was accelerated by low amounts and retarded by high amounts of 1-naphthaleneacetic acid and 1-naphthoic acid. No significant effect on abscission was observed from 1- methylnaphthalene, 1-naphthaldehyde, or phthalic acid applied in amounts from 10−8 to 10.0 μg per petiole; or with naphthalene from 10−3 to 10.0μg per petiole. Naphthaleneacetyl aspartate had no effect at 5×104 to 5×10−3 μg per petiole, but completely inhibited abscission at 5 × 10−1 and 5.0 μg per petiole. The data are analyzed on part by a previously described mechanical method for the determination of abscission indexes, and in part by a new method described herein, using a digital computer for the analysis of the abscission time-course data. The results have significance to the understanding of the variability encountered in fruit thinning by 1-naphthaleneacetic acid and related substances, and are discussed in relation to the known intermediate effects of 1-naphthaleneacetic acid in fruit thinning.