Bovine, chicken and frog alpha-macroglobulins and ovomacroglobulin were studied by circular dichroic spectroscopy over the region 205-250 nm. All four spectra exhibited negative ellipticity with minima at about 215 nm similar to that reported for human alpha 2-macroglobulin. On reaction of the alpha-macroglobulins with trypsin, the spectrum of each of the four changed similarly. However, these proteins exhibited different conformational changes when treated with methylamine. These differences were exploited to determine which characteristics of alpha-macroglobulins correlate with changes in circular dichroic spectroscopy.