Abstract An aerobic soil biodegradation study was conducted with strychnine alkaloid to evaluate loss of the parent compound (non-radiolabeled) from sandy loam and sandy clay loam soils during 2 months of incubation, and to detect non-volatile products which occurred during this period. The biologically active soil samples were treated with the strychnine alkaloid to yield an overall concentration of 10 ppm. The treated samples and controls were held in an environmental chamber under dark conditions at a temperature of 25°C and a soil moisture content of 75% of field capacity. Eight sampling periods were chosen; at each time interval, three treated samples and a control were selected for strychnine extraction and analysis using high performance liquid chromatography ( HPLC u.v. ) at a wavelength of 254 nm. Degradation of strychnine in both the sandy loam and sandy clay loam soils occurred in three distinct phases, which included a lag phase, a rapid loss phase and a leveling off or soil binding phase. It is believed that the lag phase may have been due to a microbial adaptation period combined with soil sorption. Approximately 50% of the strychnine was lost from the sandy loam and sandy clay loam soils in 24 and 27 days, respectively. Within a period of 33–40 days, about 90% of the strychnine had dissipated from both soils. The appearance of a degradation product occurred early in the study (day 7) and reached a maximum concentration at either day 14 (sandy loam) or day 21 (sandy clay loam). The initial degradates of strychnine are believed to be polar compounds with strong sorption characteristics. A discussion is presented in this paper of these possible products, together with a mechanism by which strychnine is theorized to have degraded in the soils.