Six commercial and one laboratory urea-formaldehyde (UF) resins with molar ratios between 1. 85 and 1. 05 were used in a pilot plant to manufacture 28 medium density fiberboards, 0. 9 m multiplied by 0. 9 m multiplied by 16 mm. Formaldehyde release measured with the 2 h US desiccator test ranged between 8. 6 and 0. 3 mu g/mL after six weeks. Perforator values ranged from 80 to 9. Low molar ratio resins produced medium density fiberboard with good mechanical properties while yielding formaldehyde release rates sufficient to meet the 0. 1 ppm requirement of ASHRAE 62-1981 or similar standards and guidelines for minimum acceptable indoor air quality at reasonable product loading ratios.