Dissolved and particulate nucleotide triphosphate (NTP) concentrations were measured in the upper 1000 m of the water column during 3 summer and 3 winter months at Stn ALOHA (22.75 degrees N, 158 degrees W) in the oligotrophic North Pacific Subtropical Gyre. In the euphotic zone (0 to 175 m) particulate adenosine-5'-triphosphate (P-ATP) and dissolved ATP (D-ATP) concentrations were positively correlated in summer (0 to 175 m; r(2) = 0.61, p < 0.001, n = 24), but not in winter (r(2) = 0.02, n = 24). D-ATP comprised > 65 % of the total ATP (T-ATP) pool in the summer, and similar to 50% in winter. Dissolved guanosine-5'-triphosphate (D-GTP) inventories were 5- to 6-fold greater in July and August than those observed in mid-June (1.1 +/- 0.1 vs. 8.0 +/- 0.6 and 6.5 +/- 0.3 mu mol D-GTP m(-2), respectively) and winter concentrations were on average lower than the mean summer concentrations. The particulate GTP (P-GTP) inventories were almost twice those measured in winter (mean 1.1 +/- 0.4 in summer vs. 0.6 +/- 0.1 mu mol P-GTP m(-2) in winter, n = 3). These results are consistent with higher microbial growth rates in summer. Uptake of D-ATP showed multi-phasic kinetic patterns. The half-saturation constants (K(t)) ranged from 1 to 26 nM at D-ATP concentrations of 0.2 to 30 nM, and V(max) ranged from 0.3 to 1.4 nM d(-1). At concentrations > 30 nM, K(t) exceeded 100 nM and V(max) was 10.4 nM d(-1). The calculated net production rates of D-ATP ranged from 40 to 150 pM d(-1), and the turnover time of the ambient D-ATP pool was estimated to be 1 to 2 d. The P flux through the D-ATP pool could potentially be 5 times faster than that of the bulk DOP pool, implying that P derived from nucleotides may be an important pathway in the P cycle of oligotrophic oceans.