On the basis of toxicity assays using partition centrifugation cells it was established that the sedimentation coefficient of type A botulinum toxin appearing in the lymph of orally poisoned rats was 7.9 x 10–18 cm. per dyne sec. with 95 per cent confidence limits of 4.4 to 11.4 x 10–13 cm. per dyne sec. This is a significantly lower value than that obtained for crystalline toxin but is well within the range of size for proteins. Exposure of crystalline toxin for 2 hours to digestive processes in a section of the duodenum of living rats did not significantly reduce the sedimentation coefficient of the toxin. The S20 of crystalline toxin employed in the present study ranged between 12 and 21 with a mean value of 17.9. While it was observed that both botulinum toxin and albumin sedimented from lymph in glycerol gradient tubes to essentially the same level no evidence was developed to indicate association between toxin in lymph and serum albumin. The electrophoretic mobility of toxin in lymph is like that of crystalline toxin and not albumin. Dialysis of toxic lymph against serum albumin does not result in the appearance of toxin in the dialysate.