An analog of bobine PTH [nle-8, nle-18, tyr-34 bPTH-(1-34) amide, (PTH-Ana)] which is a potent stimulator of renal adenylate cyclase has been compared with the native hormone bPTH-(1-84) and the biologically active amino terminal portion, bPTH-(1-34), for its effects on bone resorption and bone collagen synthesis in organ culture. All three compounds stimulated the release of previously incorporated 45Ca from cultured fetal rat long bone shafts with similar dose-response curves at 10(-9) to 3 X 10(-8) M. All three compounds inhibited bone collagen synthesis as measured by incorporation of proline into collagenase digestible protein, whereas incorporation into noncollagen protein was not inhibited. The effects were dose related and decreases in percent collagen synthesis were significant at 10(-9) M. Thus PTH-Ana appears to have the same effects on bone resorption and collagen synthesis as bPTH-(1-84) and (1-34) and is likely to be a valid probe for investigating PTH receptors in bone as well as in kidney.