The helix-coil conformational transition taking place in a family of poly(beta-peptide)s, namely, poly(alpha-alkyl-beta-aspartate)s (M-w > 100 000), upon addition of acid or by changes in temperature has been investigated. Results obtained for a set of optically pure polymers differing in the size and shape of the alkyl side chain evidenced that the transition is a phenomenon common to all poly(beta-L-aspartate)s. Experimental conditions required for transition were found to be independent of the constitution of the poly(beta-peptide). Investigation of poly(beta-D,L-aspartate)s with different enantiomeric composition and configurational sequence revealed the occurrence of the helix-coil transition in block stereocopolymers for any D/L ratio but not in stereocopolymers with a statistical distribution of the antipode units.