This is a call for observing proposals for the Heinrich Hertz Submillimeter Telescope on Mt. Graham, Arizona for a scheduling period from mid-September 1999 through January 2000. Facility instruments which are expected to be available for general use during that period include heterodyne receivers (SIS mixers) for the frequency ranges 200-310 GHz (one polarization), 313-383 GHz (dual orthogonal polarizations), and 430-495 GHz (one polarization). A high-frequency heterodyne receiver developed by the CfA Submillimeter Receiver Lab will be available for shared use during the Steward Observatory scheduling period. This receiver employs a hot-electron bolometer (HEB) which covers the frequency range 790 - 840 GHz. Measured double-sideband receiver temperature is 900 K. The spectroscopic bandwidth is 1000 MHz. With the latest improvements to the telescope surface, excellent high-frequency performance has been achieved for this system. A single-pixel facility bolometer for continuum measurements, and providing any one of 4 wavelength bands at 350, 450, 870, and 1300 micrometers is also expected to be operational. It is anticipated that a 19-channel bolometer array from the MPIfR will be installed for test observations during this observing period. The array operates in the 870 micrometer wavelength band, and has a typical rms sensitivity of ~1 Jy/root-second. The array may be available to observers on a test basis during this period, and is expected to be scheduled more routinely during the first trimester of 2000. Available spectral line backends include two acousto-optic spectrometers (AOSs) each with 1024 channels covering a total bandwidth of 1 GHz; one AOS with 1024 channels covering a total bandwidth of 250 MHz; and a set of filterbanks with 256 x 1 MHz filters, 256 x 250 kHz filters, and 128 x 62.5 kHz filters. Further details about the telescope and these instruments may be found under "Specifications" on the SMTO web site (http://maisel.as.arizona.edu:8080/), which is also accessible through the Steward Observatory home page (http://www.as.arizona.edu); or by contacting the SMTO staff (T.L. Wilson, Director), or (regarding the 200-310 and 430-495 GHz receivers only) Chris Walker at Steward Observatory. Receiver and spectrometer details are given in the SMTO web site. Proposals should consist of the standard SMTO proposal cover sheet; a brief scientific justification (not more than 3 pages); and a source list with observing time requirements and justification. SMTO proposal cover sheets are available from the SMTO web site (under "Observing at the SMT"), in either PostScript or LaTex format. Proposals will be reviewed by the Submillimeter Telescope TAC, appointed by the Steward Observatory Director. Scheduling of successful proposals will be done according to availability of the receivers requested. Users should expect that weather-dependent priority scheduling will be used for this scheduling period, with proposals in the 430-495 and 790-840 GHz bands given priority for observations during optimum weather conditions. Please submit five paper copies to Susan Lake, SMTO Steward Observatory (Room 488) University of Arizona Tucson AZ 85721 by Friday, August 27, 1999.