A peroxide-crosslinkable composition comprising: (A) A peroxide-crosslinkable polymer, e.g., a polyethylene; (B) A nitrogenous base, e.g., a low molecular weight, or low melting, or liquid nitrogenous base such as triallyl cyanurate (TAC); and (C) One or more antioxidants (AO), e.g., distearylthiodipropionate (DSTDP). The composition is useful in the manufacture of insulation sheaths for high and extra high voltage wire and cable.