var
  P: PChar;
  S: TMemoryStream;
  Size: LongInt;
begin
  S := TMemoryStream.Create;
  MyMemoField.SaveToStream(S);
  Size := S.Position;
  GetMem(P, Size + 1);
  S.Position := 0;
  S.Read(P^, Size);
  P[Size] := #0;
  S.Free;
  { используем текст в PChar }
  FreeMem(P, Size + 1);
end;