A 49 year old carpenter developed asthma after he was employed in a new workshop. Specific inhalation tests carried out in a laboratory with presswood sawdust and the different glues used at work were negative. Monitoring peak expiratory flow rates (PEFR) at work revealed a progressive fall on consecutive days with recovery after periods off-work. Histamine inhalation tests showed a definite increase in bronchial hyperexcitability after working periods. Monitoring of PEFR in conjunction with histamine inhalation tests can thus help in confirming occupational asthma.