evaluation of a digitonin disk assay to discriminate between acholeplasma and mycoplasma isolates from bovine milk a study was undertaken to evaluate effectiveness of a digitonin disk inhibition test to discriminate between acholeplasma laidlawii and mycoplasma sp isolated from bovine milk the test measured zone diameters of growth inhibition surrounding a digitonincontaining disk on solid medium zones of inhibition for 20 isolates of a laidlawii ranging from 814 mm did not overlap those of 261 isolates of mycoplasma sp ranging from 16 to 38 mm examination of variation in zone diameters for m bovis found that inhibition was not appreciably affected by agar dehydration zones of inhibition increased with increasing dilutions of stock culture and decreased with increasing incubation time analysis of variance and fishers least significant difference test of logn zone diameters revealed that differences in mean logn zone diameters were different at the 001 level of significance between some of the six species of mycoplasma examined indicating that growth among some species of mycoplasma was effected differently by digitonin the digitonin test was found to clearly discriminate between a laidlawii and mycoplasma sp indicating that the test would be useful as a practical screening test of individualcow and bulk tank milk for mycoplasmas