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The uptake of nitrate and ammonium by a terrestial (Bromheadia finlaysonia) and an epiphytic (Dendrobium hybrid) orchid in solution culture has been studied. The rates of nitrate and ammonium were relatively linear, with higher rate of uptake for ammonium. The rates of nitrate uptake in terrestial and epiphytic orchids were 0.4 and 0.9 μmole gm fw-1 hr-1 respectively and they were considerably lower than those of most major crops. SEM studies show that the velamen of Bromheadia was 2 cells thick whereas that of Dendrobium was 8-10 cells thick. It is unlikely that the velamen is the major factor in restricting influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) were present in roots and leaves of both orchids. NR was high in roots but low in leaves. The reverse was for GS. The activities of NR and GS was low but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid root.