Utilization of naturally-occurring dissolved free and combined amino acids (DFAA and DCAA) and dissolved DNA (D-DNA) was studied in batch cultures of bacteria from 2 shallow marine environments, Santa Rosa Sound (SRS), Florida, USA, and Flax Pond (FP), Long Island, New York, USA. In addition to control experiments, cultures were enriched with various sources of C and N. In the SRS cultures, net C assimilation of DCAA, DFAA and D-DNA made up from 42 to 60% of net bacterial C production. The average, relative incorporation of C from DCAA, DFAA and D-DNA was 0.13, 0.77 and 0.10, respectively. The corresponding values of N were 0.10, 0.81 and 0.09. Addition of NH4(+), DFAA, or both, increased the incorporation of DCAA, DFAA and D-DNA. Incorporation of N from DCAA, DFAA and D-DNA equaled 111 to 219% of the bacterial N production. Including incorporation of NH4(+) and release of NO3(-), calculated net bacterial N incorporation made up 48 and 290% of bacterial N production. In the FP experiment, net assimilation of DCAA, DFAA and D-DNA equaled 66 to 91% (average 77%) of net bacterial C production. Largely all C incorporation was due to assimilation of DFAA. (Copyright (c) Inter-Research 1993.)