Novel parathyroid hormone peptide (PTH) and parathyroid hormone related peptide (PTHrP) or derivatives thereof which are biologically active are disclosed, as are pharmaceutical compositions containing such peptides, and synthetic and recombinant methods for producing such peptides. Also disclosed are methods for treating mammalian conditions characterized by decreases in bone mass using therapeutically effective pharmaceutical compositions containing such peptides. Also disclosed are methods for screening candidate compounds of the invention for antagonistic or agonistic effects on parathyroid hormone receptor action. Also disclosed are diagnostic and therapeutic methods of such compounds.