This thesis reports the mass spectral identification and characterisation of three new groups of algal compounds. A series of novel pectenotoxins (PTXs) were identified in retained sub-samples of Irish mussel extracts that had previously been utilised to obtain bulk quantities of some other algal toxins. The first eluting of the novel pectenotoxins, when analysed on a C-18 column using an MeCN-H2O gradient, afforded MNH4+ and MNa+ ions at m/z 864 and 869 respectively. This compound was designated as PTX-i. Three minor isomers (possibly storage artefacts) of the dominant PTX-i compound were also detected in the retained extracts, together with several later eluting sulfonated and sulfonated fatty acid ester analogues of PTX-i. The dominant fatty acid analogues were found to be the 16:0 esters. Sulfonated PTX-i isomers and their 16:0 fatty acid ester analogues showed strong m/z 925 and 1163 ion responses respectively in negative ion mode. High resolution mass spectrometry (HRMS) data showed the atomic composition of the m/z 925 ion to be C47H69O17S. Full scan, MS2, MS3 and MS4 mass spectral data determined in both positive and negative ion modes for the three series of PTX-i compounds was consistent with the proposal that they possessed a C5H11O3 side chain attached to C-35, rather than a 36-hemiacetal ring system as found in other known pectenotoxins, and that the sulfate and fatty acid residues were attached to two of the hydroxyl groups believed to present in the C5H11O3 side chain. An algal water sample collected from Vigo, Spain (Dinophysis acuta, 12/12/05), that had previously been extracted with CH2Cl2 and Et2O, was found to contain low levels of two new pectenotoxin-2 seco acid (PTX-2SA) analogues that showed MNH4+ and MNa+ ions at m/z 896 and 901 respectively. Full scan, MS2, MS3 and MS4 mass spectral data determined in positive ion mode, in combination with NaBH4 and NaBD4 reduction reaction product data determined for PTX-2SA and the two new compounds, established that the new compounds were 14-hydroxy analogues of PTX-2SA. The Spanish algal water sample also found to contain an appreciable level of two glycosides which were identified from a combination of full scan, MS2, MS3 and MS4 mass spectral data determined in both positive and negative ion modes as either 7- or 24-O-glycosides of okadaic acid (OA) and dinophysistoxin-2 (DTX-2), as MSn data excluded C-2 or C-27 O-glycosylation. 1D and 2D-1H NMR, obtained by co-workers while the mass spectral investigations reported in this thesis were in progress, showed that the glycosides were the 24-β-O-glucopyranosyl analogues of OA and DTX-2. A set of three New Zealand derived algal water extracts, two from West Coast, South Island (Dinophysis acuta) and one from Akaroa Harbour (Dinophysis acuminata), were prepared and analysed for the three groups of new algal compounds reported in this thesis. PTX-i and its analogues were not detected in any of the New Zealand samples, the two 14-hydroxy PTX-2SA compounds were detected in one of the West Coast samples and the Akaroa Harbour samples and 24-O-glucoside OA and DTX-2 analogues were only detected in the Akaroa Harbour sample.