Peptide derivatives of the following general formula (I): ##STR1## wherein AAA is deletion or Ser, BBB is deletion or Glu, CCC is deletion, Ile, Phe, Leu, cyclohexylalanine, D-alle or Lys substituted at the .epsilon.-position by C.sub.6 --C.sub.18 alkylcarbonyl group, DDD is Gly or Gln, EEE is Leu, Nle or Phe, FFF is Met, Leu or Nle, GGG is Ala, Ser Leu, Asn, Asp or Gln, HHH is Leu, Glu or Lys, III is His, Lys or Arg, JJJ is His, Lys or Arg, Xaa is Ala modified at the carboxy terminal with an amino group, provided that CCC and DDD may independently be modified at the amino terminal by C.sub.2 --C.sub.18 alkylcarbonyl group, and that EEE is not Leu when FFF is Met, GGG is Asn, HHH is Leu, III and JJJ are His, and the salts thereof, which exhibit a potent inhibitory activity against hPTH and are useful as a therapeutic agent for treating dysbolism associated with calcium or phosphoric acid, such as hypercalcemia, osteoporosis, hyperparathyroidism, renal osteodystrophy, and the like, and other related diseases involving PTH or PTHrP.