In a multicentre survey of alpha 1 antitrypsin deficiency 25 heterozygotes of type SZ were identified. Fourteen index cases were identified through chest clinics and 11 non-index cases through family studies. Emphysema was largely confined to index males who had smoked and there was little evidence of the disease among the non-index cases. It appears that the SZ phenotype may carry little or no extra risk of emphysema.